Hi,
I just finished a build very similar to yours (everything's the same except I use a Sapphire HD6870) and I can't get the audio working for the life of me. I've tried using the MultiBeast drivers, but they give me a kernel panic on startup and safe mode leaves me with a white screen and I've tried those beta drivers that were recently posted and they make no problems and audio devices appear in OSX but there's just no output. Is there anything I might have forgotten?
Edit: Oh wow, I just noticed 10.7.2 is a requirement for the new drivers, I'm downloading the update now, I hope it's gonna work after I install it..