My receiver is pretty weird that way. I have the mains set to small, but I also have the option of sending LFE to the Mains, Sub or both.
I guess it sort of contradicts itself like that, but I have noticed that if I set the Mains to Large and LFE to Sub, there's not much LFE being passed to the sub.
I have the mains set to small and LFE to both right now and it sounds pretty good and adds to the LFE effect. That's why I wanted to know if the m80's would distort (Bass wise) at lower freqs then they were built for.