I've seen that some recent high-end receivers allow bridging some of the channels to increase power to those channels. I have a 5.1 system with no real intention of moving to a 7.1 system, but I'm planning on getting a new receiver for other reasons. If I were to bridge the left and right rear surround channels (6 and 7) with the left and right front channels (1 and 2), I would have more power driving my mains, which would be great for 2-channel listening. But does this have a negative effect on the center channel or surrounds when the power is unequal?