I've never seen one that would take more than two sources. I have one made by Russound that is designed to switch to multiple speakers and allows 2 sources and I could envision using 3 of their SDB 2.1 speaker selectors to allow 4 receivers to be tried by simply pushing the A/B buttons on the various speaker selectors.... They run about $150 each.

http://www.russound.com/speaker_selectors.htm