Sure, I'm currently using the ATI HDMI driver
that's included with the 9.6 driver package. That's the most current available. I haven't installed any other drivers
yet, and the motherboards onboard audio is disabled in bios, so its just the video card's audio chip producing sound.
As for codecs, I also have CCCP (Combined Community Codec Pack) installed, Core AVC and AC3 Filter.
BUT, the problem was there before I installed any codecs or even the drivers. Sound was working out of the box, but backwards :P