Attached I'm sending the snapshot of my kmix. In my opinion the problem isn't about the settings in kmix or Phonon. The problem is once you have made proper settings in Phonon, once you have tested your new settings on Phonon and you could listen to testing voice on your headset, these settings don't affect the whole system. When you listen to youtube or you use any other application with sound, the sound is beeing reproduced via internal speaker. I'm experiencing exactly the same problem with HDMI audio output. The Phonon and kmix setting don't affect the whole system either. If it is not a bug, some advanced modifications in configuration files are required. The only way for using my Logitech headset and HDMI audio output is using VLC player which is having internal settings for audio output device.