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.