OK. There are various things that you have to do so that your DSP4000 knows that you are sending it spdif.
First, go to SETUP/audio and turn the wheel so that it says "input: S/P DIF".
Then make sure that the "sample rate" field has the right number, and that it shows "S/P DIF ok".
The MUTE and BYPASS lights should be off.
Select the "Thru" preset for test purposes.
If these are all true, the 4000 is doing all it can, and the problem is probably at the DAW end.
