Hi guys. I'm sorry but my first post here is a cry for help! I'm also sorry if I'm in the wrong section!

I bought a PCI card with the CMI8738 chip, with the assumption that the digital optical input would allow me to run a TOS lead from my Xbox360 to the sound card and back out to some 5.1 PC speakers. So far everything I've tried has failed. The speakers are working fine with the PC, so they and the card are fine. I must just be doing something wrong with the optical side of it. I'm running Vista64, by the way.

Thanks in advance for any help

I had this same problem, bad news is I eventually gave up and used the Xbox stereo connections via a 3.5mm plug to the line in on my sound card.
I think it doesn't work because the digital in on the PC doesn't accept a dolby digital signal. It only accepts a PCM signal.
I'm not 100% sure about that, maybe someone can clarify.
However, I find the sound processed as dolby pro logic acceptable for games.