The following is a list of options for your Card/Codec...
ALC882/885
3stack-dig 3-jack with SPDIF I/O
6stack-dig 6-jack digital with SPDIF I/O
arima Arima W820Di1
targa Targa T8, MSI-1049 T8
asus-a7j ASUS A7J
asus-a7m ASUS A7M
macpro MacPro support
mbp3 Macbook Pro rev3
imac24 iMac 24'' with jack detection
w2jc ASUS W2JC
auto auto-config reading BIOS (default)
To test each one, do the following..
1. Close ALL sound apps.
2. rmmod snd-hda-intel
3. modprobe snd-hda-intel model=one_of_the_above_options
4. load alsamixer, unmute channels and check settings.
5. run 'speaker-test -c2 -Ddefault -twav'
6. plug headphones in/out to see if its working how you want it.
7. if its still not working, goto step 1, repeat, but use a different model= option from above.