No audio control and no surround support

The main problem is I can't change the volume from the indicator or the Settings. Also, in the settings the only option for "Output Sound" is "Headphones", even though I have an Asus Xonar DSX 7.1 sound card.

I investigated the problem, trying to use alsamixer and the channels are all there; changing them changes the volume as expected:

I also discovered that the volume bar in the indicator and in Settings are connected to the Headphones level in alsamixer. There is probably a problem in detecting the right channels to control from the UI,

This is possibly linked to [this](https://github.com/elementary/switchboard-plug-sound/issues/77) other problem

---
There is a **[$10 open bounty](https://www.bountysource.com/issues/64883906-no-audio-control-and-no-surround-support?utm_campaign=plugin&utm_content=tracker%2F59962557&utm_medium=issues&utm_source=github)** on this issue. Add to the bounty at [Bountysource](https://www.bountysource.com/?utm_campaign=plugin&utm_content=tracker%2F59962557&utm_medium=issues&utm_source=github).