KD7 Digital Audio Problem

I have a KD7 Mobo with the built in AC97 sound system. It has been working
fine with the standard stereo out to a single pair of speakers. I recently
picked up a small 5.1 speaker system that uses the digital optical port.
Stereo works fine through the fiber optics, but no other speakers work.

I've tried reinstalling the drivers, changing the speaker mode to 6-channel
mode for 5.1 speakers. No luck.

Any ideas?

Thanks!

russ