I had the same problem with my soundcard intel ICH6.
On a web site I saw this solution:
you have to modify the /etc/modprobe.d/sound file:
before:
alias snd-card-0 snd-intel8x0
options snd-intel8x0 index=0
after:
alias snd-card-0 snd-intel8x0
options snd-intel8x0 index=0 ac97_quirk=2
reboot (or unload and reload sound modules) and now the master is active, no more headphone level and I could again control kmix volume without open the entirely application.
Hope it works for you too!!!
A +
Romain.