WIP: Astro Mixamp TR gaming headset support

This fixes #109

The astro mixamp can also take 5.1 Dolby surround sound. However, I could not figure out how to make that work. While in the device is in Dolby mode, the game audio channels become completely mono. The mixamp must have DOLBY turned off in order to get working game stereo sound.

The good news here is that the default device is the chat device, is stereo and works properly, even if the sound quality isn't as good. All audio coming out of the chat device was the old behavior before this change as well.

EDIT: I'm going to work on this a bit more.