Try paman (Pulse Audio Manager) - set the levels for your devices with
it, then just use KMix to control the master levels (alsamixer only
controls alsa).
I'm a bit lost on the current status of the different parts that make up audio systems in KDE in Debian Sid. I'm wondering what is the recommended setup? Phonon, alsa, and/or pulse audio? And a adequate backend for Phonon: e.g. VLC or gstreamer?