Mac Pro - Mac Pro toslink configuration

Hey everyone!

I already own a MacBook Pro, and now i got myself a new Mac Pro 2xXeon 3.0, 8800 gt, and I'm perfectly happy with the machine apart from being unable to set up my toslink optical out propperly. On my MBP I just connected the cable and set my Vlc audio output to Built-In Digital (Encoded output) and it worked. But on my Mac Pro, it's obviously not that simple, because i've tried everything i could imagine, but still was unable to make it work. One thing that might be interesting is, that when i set the output to Built-In Digital (Encoded output), in my OSX sound properties pannel it switches to internal speaker, seems a bit wierd.

Anyway thanks for any answers.