Mac Pro: Can't get my optical audio to work!

[b3baby]

I just bought (as in 2 weeks ago) the new Mac Pro. I have a logitech 5.1 surround system with digital audio input. But it won't receive, or my mac is not sending, a digital audio signal. I think I've got everything set correctly in system preferences. Has anyone encountered/heard of this problem with new mac pro's? Is there something I'm missing?

 

[filman408]

Make sure system prefs looks like this. Digital out should be selected.
Also, the Mac Pro has discreet optical out (as sure you know), unlike the other models with combined systems.