the optical output is 2 channels when the sound card processes the audio track... but you can set the sound card to "SPDIF Passthrough (Dolby Digital / DTS Digital Out)" and use an external decoder...
When i do this i'm not sure if the reciever is really getting 5.1 or not.
But it also has analog outputs for computer speakers (7.1)- 1 for front L/R, 1 for rears L/R, 1 for sides L/R, and 1 for center/subwoofer
I was thinking of 'converting them' to RCA and conecting the RCA plugs into the analog 5.1 input (6 RCA jacks labeled "5.1 Inputs")on the reciever.
I'm not sure if it will work...
since each output on the sound card carries 2 chanels it will be messy
even if it works it won't sound great, but good enough for games
ps dvd player are not that expencive