I agree with Fins. You should hide subwoofer level controls from clients. They can only cause YOU problems.

There is no button or command, AFAIK, for any speaker level adjustment. Instead the sub adjustment is inside a menu process, and once in the proper place in the menu, YOU can adjust the subwoofer level.

There might be some way to set up the subwoofer versus the YPAO so that the client can raise the sub's crossover frequency and get some crap midbass, which is probably just what she wants. This means rotating the crossover knob on the sub, but how bad can that be? (humor)