Time to show my ignorance

When adding an additional amp to a receiver so that you can go from 5.1 to 7.1 can you set it up so that the newer amp (in this example lets say it has more power per channel than the original receiver) can power the left & right mains instead of the back surrounds?




Getting to 2,000 posts; one year at a time vp160/qs8/qs4/SVS 2000/m60/Monolith 3x200 amp