The mid cut/level control is one of the things that make this amp work for me. I always leave the function engaged on mine. Otherwise, I don't think I would find it as suitable.
After you get cozy with it, make some comments about your Mills cab.
Haven't spent time tweaking Ch2. 99% of the time I was on Ch3. I was just trying to see how much gain was on tap for ch 2+ and was pleasantly surprised. It's ok, I won't create a rift in the time-space continuum or anything