If it's of any help here's my mostly-working AppleHDA kext (latest 10.6.8 one). My board is a Rev 1.0 with ALC883 (Address 2). There are no sound assertions. Tested on 10.6.8 with 64-bit kernel.
I've updated this a little. I don't think I can get any more parts working.
I've now removed the Legacy kext (seemed kinda pointless when the AppleHDA kext had to be edited anyway). Its edited plist is now part of the kext.
Didn't work for me. I'm also on a 1.0 board on 10.6.8 64-bit, but it won't recognize the internal sound card. Not a big deal to me, as I only use my USB recording interface for sound, but still would be good to get it working as I may put this machine back in it's former home theater role.
Anybody have one of the older versions Riley posted? I'm only concerned with stereo in/out, no multichannel.