FWIW, I've done exactly that with a Pioneer SX-780 receiver, a Sansui 9090 receiver, and one pair of Pioneer Hpm-100 speakers. Just wire each receiver to the speakers like you normally would. But make sure the speaker selector switch on whichever receiver isn't currently being used is set to off before powering up the other receiver. As long as you don't forget that very important step, you should have no problems. I had mine hooked up that way for 2 years, with no ill effects.

Jeff