>> M80s -3db point is 34hz, the center is 85hz, and the surrounds are 95hz
Personally, I would start with 60 Hz for the mains, and 120 Hz for the center and the surrounds. But then move the values around for the center and surrounds to see if you can drop them at all. There are those freq sweeps on Avia, but to be honest, I always prefer real material that you're familiar with. I personally have used 120 Hz without any bass localization problems, but that is one thing to listen for. (Bass coming from the sub that should be coming from the center. The center will be easiest to tell, because of all the info sent there.) Let us know how it turns out!