Guitar -> Guitar input of the Lexicon MPXG2 -> Preamp out of the MPXG2 -> Input of the M4 -> Output of the M4 -> Preamp return of the MPXG2 -> Output of the MPXG2 -> Power amp.
By doing this, I can run certain effects before the M4 (like phasers, octafuzz, etc), and certain effects after the preamp (like noise suppressor, reverb, and delays). It's an incredible setup. I love it. I've not seen another effect processor like it. I don't need an effects loop w/ the M4 because the out of the M4 is basically where I'd put my effects if it were a regular amp w/ a series effects loop. The MPXG2 allows you to do "parallel mixing" of effects anyways, so I have the best of both worlds. If I want series...I can do that...if I want parallel...I can mix effects into my "dry signal" giving me the best of both worlds.