This is for troubleshooting purposes only, and not intended to connect it like this to make it work directly, but here's what I'd try:
I think you said you have a computer with a MIDI interface on it.
If it's a Mac, install a free application called "MIDI Monitor":
https://www.snoize.com/MIDIMonitor/If it's a PC, install a free application called "MIDI-OX":
http://www.midiox.com/app.htmConnect the MIDI Out from your D8B to your MIDI in on the computer. In either MIDI-OX or MIDI Monitor, make sure that the MIDI port you connected your D8B to is active.
Press one of the Transport control buttons on the D8B. MIDI Monitor/MIDI-OX should show that it received some sort of MIDI command. Probably labeled something like a MMC command (MIDI Machine Control).
If this works, disconnect MIDI between the D8B and the Computer, and instead connect the MIDI Out from your HDR to your MIDI in on your computer, and repeat the same thing above.
Does MIDI-OX or MIDI Monitor receive the same kind of signal (MMC) when you press one of the transport control buttons on your HDR?
If the signal does NOT arrive from one of them, then there's something wrong with MIDI functionality. Could be the external adapter that goes to the 9-pin port, could be the MIDI card, etc.
I'd suggest trying this first, then you at least know if MIDI generally works.
This won't work if you still get the "Error 43", though. That would need to get resolved first.
I'd suggest trying this, and then reporting back. Then we can take it from there.
Good luck!