No subject

stereo but it's a very basic downmixing.

Myth can do upmixing and downmixing for you with much higher quality algorithms.

Myth doesn't show the other audio device, because they are all in use.
Make sure when running mythfrontend that you turn off any application
using audio ...

You can override the myth auto-settings, type in the audio device:
ALSA:hw:0,0

make sure AC3 and DTS are unchecked if the fields appear, and set it to Stereo

This will let myth do the downmixing, you will get a much better
result than using your alsa dmix

If you want to use your original dmix (ALSA:default) you will need to
set up the speaker as 5.1 because of how you've configured ALSA.

JY