Audio Systems: Overheating Speaker Selector Problem, hook wires, internal crossover

Question
I have six home stereo speaker sets (throughout the house) running through a Sonance SS6 (Speaker Selector - 6 channel) unit. When 5 of the 6 sets are activated everything works fine.

Problem:
When the 6th set (master bedroom) is activated the volume from the other 5 sets decreases and the Speaker Selector unit heats up like a toaster oven. One unit has burned out already.

I have re-arranged speaker wires but the overheating and decreasing volume problem only happens when the master bedroom speaker set is activated.

What could the problem and solution be?

Thanks,
Justin

Answer
you need to verify that the wires to the 6th set didn't get a 'staple short' during installation by disconnecting them from speakers and selector box, and check wires with ohmmeter for short or low resistance. if they check ok, hook wires back up to selector with no speakers and power up. if selector still heats up, wiring or selector is bad. also, if small size wire is used, that alone could be the problem. small wires mean no more than low volume. also switch speakers with another set to verify internal crossover in 6th set haven't shorted.