Midi on the Quad might let u combine any channel with another, or a midi interface running 1/4" jacks on the quad.Ive tried it,that was decades ago,I can't remember if I liked or not.Back I'm the day I do remember stepping on 2 chls at once on the fu2 pedal and getting both on.
My fav poweramp for the Quad would be the 400,500 or vht 292 & 2150.