Horse Hockey. You can turn the gain up all the way. The protection circuitry in the speakers should protect them. If you start to hear audible distortion or noise when no signal is coming from the receiver, then turn the gain down until you don't hear it any more.
I leave the gain on my EP-4000 up all the way all the time and I don't hear a thing(except for the fan that is).
Television: Mitsubishi WD65737 DLP
Processor: Emotiva UMC-200
Amps: Carver AV 806x/Behringer EP4000
Mains: DCM TimeFrame 600 Center: AT 453C
Surrounds: AT 251.1 Sub: Danley DTS-10
Blu Ray: Panasonic DMP-BD655