Watching someone struggle with volumes and sound selection while trying to play at the same time is usually a good indicator of whether something is easy to set up in advance or not. Generally, you'll see those people with easy to use OS's doing the least adjustments while they play, whereas someone constantly fiddling live (and getting in the way of the playing) seems to indicate that whatever settings need to be made that ease this burden were more bother than they were worth...

It's not just whether you can DO something - it's whether doing it is a PITA or not.

And, I'm sorry, but I tend to divide playing an arranger into two different things. One is working the controls, and the other is actually PLAYING music. The more you have to do the former, the less you can do the latter. Basically, if you have TIME to mess around with the sliders, buttons, what have you, you simply aren't PLAYING very much...