Xbox Sound
The Xbox ALSA driver is unable to control volume through hardware which is a pain. You can get around this by defining an ALSA slave device which manages the volume through software and appears to client programs as if it's a real piece of hardware.
Create a file /etc/asound.conf (if you want the new device to be visible to everyone) or ~/.asoundrc (so it's visible to programs started by the mythtv user) and add these lines:
pcm.softvol { type softvol slave { pcm "hw:0,0" } control { name "Master" } } pcm.dsp0 { type plug slave.pcm "softvol" }
this tells ALSA to create a "softvol" device which you may then access in myth by specifying "ALSA:softvol" as your audio device, "default" as the mixer and "Master" as the mixer control. Audio settings are in the Utilities & Setup -> Setup -> General -> Audio page.
Alternatively, you can include the following additional lines:
pcm.!default { type plug slave.pcm "softvol" }
And ALSA will use softvol as its default sound device so you can simply tell myth to use "ALSA:default". Be aware that other ALSA-using programs will be affected too. Some, like xine, default to PCM as the mixer control so you'll likely have to change their configuration accordingly.