there are a couple of devices which allow you to switch between different amps, and i think route your signal to more than one at a time. i know Morley make one, it's actually got George Lynch's signature on it! and i remember seeing one on one of the boutique pedal makers' sites, HBE or Toadworks.
i have heard guitar being played through two amps at once, one heavily distorted and one just overdriven, and it sounded great. and good ole Diamond Darrel used to record with three amps, one each for bass, mid and treble.
don't know if that's any help, but it's what i got 8)