enable a stereo output path(in Setup>IO>Output tab) and assign it in the grid matrix. Then set tracks to the SPDIF output(and remember that you can rename the outputs). The question is, with the Mbox volume knob actually control the digital out, or will you have to adjust your speaker volume from inside the session
Also, if the speakers have both SPDIF and analog inputs, I would compare both to see if you can even hear a difference
