Maybe there's some confusion here....
I don't channel switch ever. The heads are set to the settings I like, and I pan between them using an Ernie Ball Stereo Pan Pedal.
I don't want to A/B them ever.
For bigger shows, I use 2 DR's, each with it's own dedicated 4X12, and pan between them to "build" songs up or down.
For smaller shows, I use a TOV combo for dirty, and a 65 Fender Twin Reissue for cleans.
In this scenario, I want to run my MarkIV AND my Dual Recto at the same time, each with it's own dedicated 4X12 cab.
I'll still run another head with it's own cab just for cleans.