@Mr.Robot, I’m a little lost as to what the issue or issues are or what you’re trying to accomplish. Can you summarize where you’re at?
My sliders work, and the volume changes between zero and 100%. Mute is programmed to set the volume to zero. When you say your sliders are out of sync, where are you observing this? Are you talking about a single output or your master slider?
I don’t know much about music assistant, but from a quick read, it streams music to a device, so you would need a device connected to C4 to stream to. I didn’t see anything about outputting directly from home assistant. I use a Sonos Play connected to my C4.