I would suggest small on the m80s with just LFE (not +main). Crossover anywhere from 40 - 80hz, whatever sounds best to you.

You could also experiment with the LFE+main setting to see if you like the results but I found that it was too much "double bass" for my 3808, m80, and ep500 combo.

I would not recommend setting m80s to large allthough I think with the +main setting it doesn't matter if the fronts are large or small but perhaps I am wrong there.

-David