in my netbook i have a alc295, i don't have much channels there but i can add some to that list, i see on that list volume levels for a 2.1 setup with front left, right and center, master and pcm and other channels, you could try unmutting all channnels and trying again with vlc the way i described before
also see if kmix mixer is not showing all the channels and what others you can add to set volume levels right