I had this problem some time ago. I think I fixed it in pavucontrol, where for some reason it had got set to mute. I find alsa mixer very opaque also and remember struggling with it.

Anyway thinking about this, I just reinstalled Debian, so I ran amixer to see what mine says, and its just this:

Simple mixer control 'Master',0 Capabilities: pvolume pswitch pswitch-joined Playback channels: Front Left - Front Right Limits: Playback 0 - 65536 Mono: Front Left: Playback 65536 [100%] [on] Front Right: Playback 65536 [100%] [on] Simple mixer control 'Capture',0 Capabilities: cvolume cswitch cswitch-joined Capture channels: Front Left - Front Right Limits: Capture 0 - 65536 Front Left: Capture 65536 [100%] [on] Front Right: Capture 65536 [100%] [on]

This does work. Its much simpler than yours. I don't have a mic installed on this machine however, and my headphones are driven off a headphone amp which is fed over spdif.

Have you got zoom installed? And is it still a problem with zoom?

I remember also getting a systematic walk thru on diagnosing the problem, I think it was here:

http://www.troubleshooters.com/linux/sound/sound_troubleshooting.htm

The other thing that occurs to me is, try booting from a 'live' distro like Puppy, or a live version of Mint, and see if that helps. At least that rules out hardware and it gives you a working configuration as a reference.

I know it took me quite a lot of fiddling to make it work, and I am not really sure what did it, apart from this vague recollection on pavucontrol. Which I don't seem to have installed now on the new install.

I think I also found some material by Carla Schroder which helped. It was a struggle, and I never did get clear what had caused the problem.