Version:           3.7 (using KDE 4.4.95) 
OS:                Linux

As already discussed on IRC with Colin Gutrhie (a while ago), I think that there should be a possibility to let kmix switch the default mixer when a different sound card is the new default. 

Usecase: A user might use an USB soundcard. It has a higher priority as the default internal soundcard, therefor KDE switches playback to this card as soon as it is connected. However, kmix does not, so the default volume up/down keys (e.g. on a notebook) still control the internal soundcard volume. The user has to click on kmix and choose a different default mixer control when he connects the USB sound card. 

Reproducible: Always

Steps to Reproduce:
Plug in a different sound card with higher priority 

Actual Results:  
kmix still controls the volume of the other souncdard

Expected Results:  
kmix should control the volume of the new playback device

I am aware of the fact that KDE allows different default playback devices for different kind of sources (e.g. multimedia, system messages etc.). 

This might be an usability question, but in my opinion it is not really good usability as well if the user has to change this manually each time he conntects a USB sound card