Aschar binary patched the AppleHDA.kext in Snow Leopard 10.6.4 so it will support the ALC889 audio chipset. If you've got this chipset, then you need this file to get audio back in Snow Leopard 10.6.4

Instructions:

Download AppleHDA.kext
Open Terminal and type these commands:
sudo cp -R AppleHDA.kext /System/Library/Extensions/
sudo chown -R root:wheel /System/Library/Extensions/AppleHDA.kext
sudo chmod -R 755 /System/Library/Extensions/AppleHDA.kext

Wait about 15 minutes (kextcache needs to rebuild) or use pfix to manually rebuild cache, then reboot and you should have audio back!
Notice: You might need to manually remove caches, use this command: sudo rm -rf /system/Library/Caches/com.apple.kext.caches