SN26P - Cant get digital 5.1 to work

I just recently got the Shuttle XPC SN26P and hooked it all up. I've downloaded the latest drivers from their site. I've tried both the Coaxial digital and the Optical digital outputs on the back and I get sound, but only 2 channel stereo sound. When I play a DVD that has 5.1 DDS or DTS, it wont play it on my stereo - only 2 channel sound. I've looked around in the sound settings in Audio Deck. I've selected 6 channel 5.1 sound. In advanced controls, I have Enable Digital Output checked and its on AC3 and PCM with Auto. What else do I need to do to get the surround sound to work?

Thanks

anyone?