It is possible that you would get more heat gain from the main and center channels than the surrounds, so your placement makes sense. I don't know how much more heat gain will actually be experienced, as I've always had a hard time getting solid numbers on real world heat gain from home theater equipment, but I would expect it to be marginal (a few degrees) -- unless you were in stereo mode and the surrounds weren't even turned on.

As for rotating the role of the different amps, I have no idea. I haven't ever heard of folks rotating which channels of a multichannel amp serve which speakers, which would be very similar to rotating the assignments of different monoblocks, and I don't know what real world benefits you might see from taking the time to juggle wires that way. It is an intriguing question, though, and I'll be curious to see what others think about it.

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