Can I hook up two amps to the same speaker?

Could I hook up two receivers, each with their own source to the same speakers, and play one receiver, while the other is powered down? Now, if that is a no, is there a way for me to run and integrated and a receiver into the same speakers and play each one individually. Each, again, with their own source. If this seems ludicrous or insane; please be gentle with me...lol..peace, warren :)