Still have an issue on this microphone problem... I'm not sure if it is due to motherboard software or riderunner itself.
I muted the line as you suggested but everytime I use volume controls on rr mixer, expecially when turning volume up starting from zero, the muted line automatically unmute itself!
I tried to look for a rr command to mute permanently some line and found the "exec;mute" that maybe can help. Don't know where to use, I'm still trying to understand why the muted line unmutes itself with no reason and no request by me!