Ok, maybe I am being silly here, but I think I read that the mac pro pushes 5.1 out of the optical port. So I finally found my optical cable and hooked it up to my Sony 5.1 Receiver (I tested the cable from the Denon DVD first and surround is perfect). I have a bunch of surround test wavs that I use (FR, FL, Centre, RR, RL), but only the FR, FL and Centre are being directed out of the correct speakers. The RR and RL still comes out of the FR and FL speakers. I am a bit confused as I cant seem to find any config for the surround output. Does anyone here have an idea as to whether I am mistaken about the audio capabilities or if I am missing something?