Sorry to disagree, here, but you need none of the things David mentioned, to use the D8B as a "controller only" with Pro Tools.
All that's needed, is the D8B console and rack unit (which is also the power supply). You don't even need a DB25-to-DB25 cable, that usually needs to be connected when using the D8B as a mixer.
When using the D8B as intended as a mixer, then the computer portion of the rack unit needs to be able to successfully boot up for it to work as a mixer... but not even that is necessary when using the D8B with a ProBox as a controller ONLY.
The rack unit needs to be there to provide power to the D8B console, and you connect the DB25 cable that is attached to the ProBox, directly to the back of the D8B console.
Then connect the USB cable end of the ProBox to your computer.
Then you need to add 3 HUI controllers in Pro Tools, make sure the ProBox is set to operate in HUI mode and configure the MIDI ports the ProBox shows on your computer inside Pro Tools (no need to install a driver for the ProBox - it's "class compliant" meaning it works with your computer's built-in drivers).
I think this is why the D8B is popular to use as a controller with a ProBox... the D8B is kind of difficult to keep working as a mixer once it starts acting up... but if it does and "dies" as a mixer, it can still be used as a controller via the ProBox, as long as the console hardware itself isn't defective.
I used to think that you can even take the mainboard out of the rack unit, as long as the power supply components are still there, but this is apparently wrong. The mainboard needs to be there, for the rack unit to turn on and stay on, and provide power to the console... but that's it. It doesn't have to be "working," otherwise.
A separate ProBox forum can be found on d8bforum.com btw... but you have a higher chance of people responding over here
Be advised, that you can NOT use the D8B to route audio between the D8B and Pro Tools, when used with the ProBox. It will really be ONLY a controller (plus some functionality similar to a Mackie Big Knob... so, a monitor controller and software control surface).
Some people think that adding a ProBox will magically send 24 audio tracks back and forth between the D8B and your computer, but that is NOT the case. This sort of setup would require a quite elaborate setup with an audio interface (or multiple cascaded ones) that allows for 24 or more inputs and outputs.
But as a controller ONLY, you need the D8B console, the rack unit, the ProBox and a regular power cable. Nothing else (no mouse or keyboard, either... the D8B console can be missing ALL cards, and it will still work as a controller).