lately my receiver has kicked off, i guess in protection mode, a couple times. hasn't ever done it over the last couple yrs, so this is a concern. it seemed to happen when i was playing something loud. most recently, a couple movies. yest, eg, it shut down, and i started it back up after a few min rest. i was running only the center channel, with no rear speaks connected, and using preouts to an amp for left and right. could not having rears connected, but running 5.1 setup cause an overload or whatever to trip the protection? i assume the rear channel amps are on, but no speakers being driven. is that the reason? manual doesn't cover this.. thx!