Hmmm,
I was talking a passive easy-in easy-out volume pedal, not a dedicated TRS type pedal that connects to a special jack. You can get a stereo volume pedal (Roland used to make one ... I think they still do)that has 2 ins and 2 outs. They are passive inputs and require no additional worry or connections. Use "Y" cords or sub mixers ... it won't matter. Just plug and play - couldn't be simpler.