I am going to audition a couple of integrates and would like to flip back and forth on the same set of speakers. Would it work to wire two amps to one set of speakers (same posts) if I were careful to have one amp powered up at any given time? Or would the other set of wires give a place for the juice to go even if they were off? Would this be a danger to either amp or the speakers? The more I think about it, the more it seems like a bad idea.
Bad idea, a receiver and speakers are an electrical circuit, you have no way of controlling which wire the current flows back through. Easy way to fry an amp.
that's what the switching boxes that stereo stores are designed to do... namely switch back and forth between different sources. A/B listening with amps is very important as the sonic differences are so slight compared to speakers.
even better, audition the amps with the exact speakers you own or want if possible to hear how they mate to the amp.