I tried AppleHDA.kext from 10.6.2 - 10.6.6, still failed to get HDMI audio to work. I always get:-
I would like to tell you from my experience. I updated OS X to 10.6.6 and tried to used old AppleHDA.kext (10.6.4) and then I could not get HDMI audio for my HD5770. After that I got to use AppleHDA.kext v1.9.9f12 and then I got HDMI audio again. I was thinking that ATIframebuffer might be related to AppleHDA.kext in some way but I had no idea how. In contrast, I got to use old AppleHDA.kext (from 10.6.2-.4) for my GT240 to get HDMI audio after updating to 10.6.5-.6. I hope bbc9 can find out something.
Sound assertion "0 == hdaGfxCandidate" failed in "/SourceCache/AppleHDA/AppleHDA-179.1.4/AppleHDAController/AppleHDAController.cpp" at line 889 goto ExitI think you probably right on the relation between ATIFramebuffer & AppleHDA. I already tried 10.7 AppleHDA.kext. It just failed to load. I guess I have to wait 10.7 (official) to get HDMI audio working.