In my live application machine B is used as a guitar rack, and Machine A is a Vocal rack. Midi tweaks allow me to program and control both and leave the mixing to FOH.
I have a center dry Guitar cabinet with is mic'ed and two full range speakers for delays/samples/and reverb with direct outs to FOH. Pitch Fx needs to hit the tube power section and speaker cabinet to sound natural. I must say…I've been stuck for awhile now on how to make this application work. Really stuck.