The trouble with the Fasttrack Ultra 8R, is that the concept of that device isn't a "standalone preamp/converter unit" but it is a USB Audio Interface. The idea for that product is, to have 8 Pres available, that route their signal straight to a connected DAW computer (the main use for this device, isn’t really to send signal from the pres/inputs back out to other gear like the D8B, but just to the computer)
I used to have an 8R, but don't recall how it did monitoring. I'd expect that there's some type of real-time monitoring control-panel, that allows you to route the inputs from the Pres, back out to "somewhere" (e.g. Headphone Jacks and Main Outs), so you can hear yourself while recording, but without latency (and without any effects etc. from your DAW... the signal is being sent out at a point in the signal flow BEFORE it is sent to the DAW, so you cannot have DAW effects at that point, even if you wanted to).
If that control panel allows you to route the Pres directly back out to their corresponding line-outs (e.g. Pre 3 goes to Line Out 3), then you could connect the analog outs from the 8R, to the analog inputs on the D8B. But there's a good chance that the 8R only allows you to route the signal out to the headphones and main outs... and if that's the case, you'd really only get to use 2 of the 8R preamps at the same time, and route them to the D8B.
But even if this works (monitoring on "direct" line outs OR Main Outs), there are SEVERAL downsides to this approach, when using a USB Audio Interface like the 8R, that doesn't have a digital output:
1. Superfluous conversions that have a negative impact on audio quality. If you go into an 8R pre, and route it to it's analog outputs, then go into an analog input on the D8B, you already went through 3 conversions of the signal before you even hear it (into pre, conversion to digital to hit the monitoring panel in the 8R, then conversion to analog to go back out to the analog out on the 8R, and a third conversion back into an analog in, into the D8B, where it gets converted back to digital). You’re not likely to immediately notice a signal degradation, and maybe you’ll be happy with the results… but this is FAAAAAAAR from best practice.
2. Superfluous pres: Unless you're going into the (unbalanced - thus prone to interferences) inserts, the analog inputs on the D8B will pass through either another Pre-amp, or at least an OP-amp, to allow you to boost/trim your line level signals. Ideally, you'd want to go into an analog pre-amp, and hit a good (non-D8B) converter right after, before going into the D8B digitally. Everything else involves an additional "gain stage" that is technically superfluous and at best and doesn't contribute positively to the signal quality (probably makes it worse). More likely is a negative impact of running through two "gain stages" like that, for no added benefit. Going through 2 pres for no reason, is more likely to result in an immediately audible difference (but probably still relatively subtle).
3. The pres in the 8R aren't that great, either. It's barely an upgrade from the D8B. So, with what I'm saying above, IMO it's not worth to jump through these hoops, to get to use a marginally better preamp, than what's built into the D8B.
Long story short: The 8R is not the right interface, to tie the D8B in with your DAW workflow, in the most efficient way, and also not a good choice for a pre-amp to connect directly to the D8B.
As the Dok said above, the best way to go in, is to bypass BOTH, the D8Bs outdated converters AND it's unimpressive pres, by connecting any external pre to the D8B "digitally".
If you only need 2 pres at a time, and if the 8R allows you to route the incoming signal via the Monitor panel, to the S/PDIF output, then you could connect that to the S/PDIF input on the D8B and record through that.
This will bring other challenges with it, though... ideally, the D8B and 8R should then have their Word-Clocks synced together, or there would be a "different" kind of audio degradation (aliasing, possible pops, etc.).
Having said that, to avoid audible word-clock sync issues from “unsynced” devices connected to the D8B's S/PDIF input (e.g. a common such thing at the time when the D8B was new, would be to connect the digital output from a CD-Player, that CANNOT be synced to outside clock), the D8B resamples everything that comes into the S/PDIF input by default... which is another thing to avoid in my book.
So, while going out the S/PDIF on the 8R and into the S/PDIF on the D8B "may" get you somewhat better results than the D8B's built-in pres/converters, it's still not as good as it can be, unless everything is word-clock synced together, and the S/PDIF resample feature is disabled (I'll have to look if that's even possible... I think it ALWAYS resamples... I generally avoid the S/PDIF input on the D8B as a result. The S/PDIF OUTPUT on the D8B is safe, though, and doesn’t resample… I’m using the S/PDIF OUT all the time… I’d just turn that old dithering algorithm off, though and do the dithering with something more contemporary, if you HAVE to come down to 16 bit or something).
The best way to go into the D8B digitally, is via one of the 8-channel digital ports on one of the expansion cards. So, whatever you have available... ADAT, TDIF, AES/EBU... the audio quality going through those is absolutely identical (if anybody tries to give me a AES/EBU is higher quality, I'll “byte" your head off... the difference in the digital signal is a status-bit, that has nothing to do with the audio quality... it's otherwise, the 8xAES/EBU ports are identical in signal quality to multiple S/PDIF streams).
So, the best way into the D8B, while avoiding both, it’s pres and converters, and while not going “unbalanced,” is to use an external digital pre-amp, that has a multi-channel digital output.
On the higher-end side of things, there’s converter units like the Lynx-Aurora (n)… that’s what I have my eyes set on, but don’t have the funds for. You could get an AES/EBU expansion in those, and connect it to an AES/EBU card on the D8B.
The more cost-effective way, is to get a Pre/Converter unit with an ADAT input and output port on it. The cheapest one of those, that works standalone (i.e. not necessary to run a computer with a DAW, to be able to use it), is the Behringer ADA8200. I never owned one, so I don’t really know how they are… and I’m personally allergic to anything Behringer, so I wouldn’t know.
I’m personally looking for another old M-Audio ProFire 2626, because I had one of those, and they work great in standalone mode, with all the settings I need for that (clock sync, input/output routing is flexible, etc.). However, most of the used ones have their Firewire chip burned out, and you need a FireWire based computer, to make the standalone settings… at least initially.
Quality-wise, the pres in the 2626 aren’t all THAT different from the 8R, but IMO, they’re still a bit of a step up (I think Marketing at the time claimed the 8R pres are “Octane” pres, too… but I’m pretty sure it’s a different chip).
Speaking about the ProFire 2626… I do have an actual M-Audio “Octane” preamp, which is where the 2626 pres get their name from. That pre is nothing to write home about, but it sounds clean. So, for 8 channels of clean/sterile inputs and clean conversion, it’s a decent unit. However, you don’t get any RETURN channels to send back to the unit… I like to place these ADAT units in a way, where they’re close to where I’d record “the talent” - so, I’m missing to be able to send the monitor/headphone feed BACK to the ADAT device, so I don’t have to run yet another cable there.
So, if shopping for a front-end pre for the D8B with a digital output, I’d make sure it doesn’t only do AD-conversion and pres, but also does DA-conversion and allows you to bring signal back to the ADAT unit.
What the Dok mentioned about the digital patchbay… if you add a digital patchbay in, you can choose with the push of a button, what bank of 8 channels is being connected to the D8Bs TAPE I/O or Alt I/O cards.
I have it set up like this, too, and can choose via a digital patchbay, if I want 8 return channels from my DAW going to channels 25-32 on the D8B (I usually have my drum-track returns from the DAW going to those channel), or if instead, I can have 8 channels from my electronic drum kit going into D8B channels 25-32… so I can record MIDI drums, while monitoring them without latency (…and I can later replace this with a drum plug-in, and send THAT to the same channels on the D8B, instead. Works the same with “real” recorded drums for the return channels, of course).
I use a M-Audio Digipatch Patchbay for this, but am also on the lookout for the Frontier Design Group “Apache” digital patchbay, since that has twice the number of optical ports, and would allow me to make more ADAT ports going into the D8B “switchable"
The downside of using the Tape Return layer on the D8B to record your inputs, is that you can only go IN on D8B channels 25-48 (or via the ALT-Return), and can't use the first layer in the way the D8B was designed (i.e. with a traditional inline-console workflow, you'd normally have the Inputs come in on layer 1, and a return from the tape-machine/daw on layer 2 on the same relative channel). But when it comes to the audio quality, IMO, this is the only viable way to justify still keeping a D8B in a modern, professional level setup, without it having a negative impact on the final quality of your mixes.
Personally, I still use the first layer on the D8B, but not for recording. I have all my synths and some outboard gear returns connected to that layer (or at least defaulted to/normaled via the patchbay), so I can monitor all that gear in real-time. However, I'm not even using that in mixes, and print stems of these signals before mixing, by patching them to better pres or going directly into my audio-interface/daw to print the stems, before starting to mix (and then I sub-mix that stuff on the computer, before sending to a stereo-channel on layer 2 (Tape). My track-layout on the D8B during recording and mixing is very different).
For recording a single channel or two, I usually connect straight to my audio interface, but route the signal out via the interfaces Monitor Panel, to an ADAT input on the D8B. For monitoring that, I always have 2 channels reserved on the "Tape" layer on the D8B for my live-inputs, and so I can control my latency-free monitoring signal from that "input channel" and apply real-time effects without recording them, etc. (When working on music by myself, I have a bass connected to one input and a guitar to the other, so I can switch and hit record any time I want).
So, basically, I have a separate return-channel on the same layer, where the recorded signal is being returned from the DAW. So, what's usually done in an inline-workflow on a separate layer, I do on the same layer on a separate channel on the same layer.
(This approach of course won't work if recorded a lot of channels at once... but I can route up to 8 channels latency-free back to the D8B for monitoring thanks to my Apollo 8's DSP. Here at my home-setup, I didn't really need to monitor more than that).
Sorry, I wrote waaaaay too much again. The short version of all of this is this:
I’d forgo the 8R and would look out for a Pre/AD/DA unit like a Behringer ADA8200 (if it’s a budget question and if audio quality and reliability isn’t the #1 concern), or a “used” unit like an M-Audio ProFire 2626 that fully works. However, integrating one of those in the best possible way, will require proper word-clock sync between the devices, and you need to understand a little bit how the signal flow in the D8B needs to be changed, to be able to route this to a recording channel. But if what I’m saying in this paragraph doesn’t sound like a challenge to you, then such a Pre and AD/DA unit with ADAT I/O, that can be used in STANDALONE mode (without having it connected to a computer to use it), would be the best choice and result in the best possible audio from the D8B, since it lets you avoid it’s pres and converters… albeit while having to use the D8B with a different workflow (i.e. recording from the Tape layer), than originally designed.
Having said all of THAT… since I don’t usually record through the D8B, but mostly monitor through it, the MAIN pre-amp I use for most single channel and 2 channel recordings, is a Aurora Audio GTQ2 Mark III. This one:
https://www.auroraaudio.net/product/gtq ... o-mic-pre/It’s basically, an updated Neve 1073. Most of the time when I record, I patch it to one of the line-inputs on my UA Apollo 8. Sounds great, and IMO much better than using UA’s “virtual" pre emulations (they can get a bit blurry, IMO). UA’s plug-ins are awesome, but IMO, anything you throw a big dynamic range at, like compressors/dynamics and pres, better happens on the ANALOG side, BEFORE converting to digital. After conversion, your headroom is severely limited (in comparison), so I don’t really get the point of a lot of these virtualizations. Anyway… getting carried away…
Phew… I gotta go and put my fingers on ice for a little, after typing all of this, haha! I hope it’s somewhat useful, at least and doesn’t just read like an endless ramble. Sorry, if so!