adjusting the sound settings to only work with 2.0 Sound of my PCI card with a CMI8768 chip was a piece of cake. Controlling the master volume works out of the box, therefore keyboard buttons are usable, too.
However, when I switch to 5.1 Output, I can’t adjust the master volume for all other speakers except for FL and FR. Even setting the master to 0 has no effect on Center, RL, RR and SW, which continue at full volume (estimated). I can control the volume through alsamixer, adjusting the PCM volume and keeping master volume at 100%.
I don’t think that this is intended to work like that, also because I can’t use my keyboard buttons with it. Furthermore I’m not sure if the PCM settings are remembered across reboots.
(This is probably not specific to Antergos as I had the same issues with Manjaro and would probably also have it with every other Linux distro, I just didn’t know where to ask for advice.)
So, how do I fix the master volume to also influence Center, RL, RR and SW?