I have a different problem to yours with kmix and my audigy 2, in that
what is supposed to be the balance control does nothing when you move it
to the left, but fades the volume to zero when you move it right (and
then won't restore the volume when you centre it again). Although I have
not found any of the other various mixers for alsa to be completely
satisfactory, I have not been able to duplicate this particular problem
with any of them, which suggests to me that kmix has some problems
peculiar to itself. So it might be worth your while trying another mixer.
I have got better mileage out of kamix myself. However when I am
completely stuck I use gamix. It's not pretty, and many of the sliders
aren't labelled (at least not for the Audigy 2), but it should allow (or
at least it allows me) to control pretty well every mixer parameter on
your sound card.