Hey,
I had the same issue with sound as you had (can change volume, play music in itunes, but no sound output), here is how I fixed it:
1. Don't know if this is necessary step, but anyway
- Download fixed AppleAC97AudioVIA.kext from pattjin's thread
- Replace /System/Library/Extensions/AppleAC97Audio.kext/Contents/PlugIns/AppleAC97AudioVIA.kext/Contents/MacOS/AppleAC97AudioVIA
with the one from the pattjin's fix.
2.
- Go to Applications/Utilities/Audio MIDI Setup.
- Set Default Output to "AC97 Audio (PCM)".
- If you see "Output is not supported" text on right side of window, then in Properties For you need to select second "AC97 Audio (PCM)".
- In Audio Output options select Forumat: 48000,0 Hz.
I found that with 44100,0 Hz (default) you will hear an awful tearing when playing sounds.
3. Make sure you have your speakers plugged in to the pink (microphone) jack.
After this I had a full working stereo sound. Only problem is that I can't get mic working now since mic jack is in use...
Hopefully that helps