If you usePulseaudio, Alsa is still underlying. Depending on the apps ability to work with Pulseausdio, the following happens:
Soundsource → PulseAudio → ALSA-Driver → Hardware
or
Soundsource → Alsa → Pulseaudio → ALSA-Driver → Hardware
Anyways, to get your keys to do what you want, you should read about xev.
greetz
devil