I have a 7 channel amp, a pre/pro with dual center outs and a biwire center channel also. I bi-amped the center for awhile like you were planning. Did not really make a difference except make it play a little louder. I had to turn it down in the setup menu. Use the extra 2 channels for a second zone. Or, if the the amp can be bridged down to 3 channels, you could get some extra power to your surrounds.
Good luck,
Good luck,