I had the same problem after updating to 10.6.8 of no audio with my Gigabyte GA-P55A-USB3, F9 motherboard (Rev.2). I deleted all of the audio extensions in both the System/Library/Extensions folder and the Extra/Extensions folder.
I added the new DSDT file for my motherboard into the Extra folder and then ran Multibeast 3.7.3 and added the Unified ALC8xxx driver and the Apple HDA rollback as well as the System Utilities.
That has gotten me sound, at least, though System Profiler sees it as an Intel onboard audio processor and the Audio Midi utility sees the speakers as being Quadrophonic as opposed to 5.1.
I'm working on figuring out how to re-enable 5.1 audio, but at least I have sound for now.
Good luck.