R, welcome to actively posting(almost three years after you joined)and owning those fine M22s. Sure, each channel uses separate output transistors and the center channel may be damaged. It could also be farther up stream and even the pre-outs from the pre-amplifier don't work. You may not have anything to measure the center channel for an output, but does your father or someone have a powered sub that you could borrow briefly? You could connect the center pre-out to the sub to check for sound.

You can get great enjoyment from two M22s up front forming a "phantom" center. I'm not familiar with, and haven't looked up the 656, so I don't know if it has back surround channels, but if it does, you could use the other M22 as a center back surround in a surround processing mode.

Enjoy the music, not the equipment.