It's possible for devices with switch mode power supplies (which is just about everything these days) to cause huge voltage spikes between other devices when they are connected together. Enough to blow out an input or output circuit. When connecting receivers to amps the power should always be disconnected, not just in standby.

Pioneer PDP-5020FD, Marantz SR6011
Axiom M5HP, VP160HP, QS8
Sony PS4, surround backs
-Chris