Sound has been a royal pain to get working on this machine.
OSX 10.6 Snow Leopard and 10.7 lion both have problems.
This one died on me with my last software update.
The key is to use multibeast and to make sure you enable only the exact hardware in the Non-DSDT HDA Enabler and to remove all Voodoo kexts and HDA enablers in your extensions.
My card is a 887, so I selected 887/888b
If you have ANY others selected, your sound will break and the machine will falsely identify your card as a 892 or some such.