I have my M-60's set to small, and the crossover set to 80 Hz for all speakers. These settings work well for me, and it is what is recommended by THX, for what it's worth. Bottom line, you may want to try a lower crossover point for your M60's (60 hz), or set them to large and see what sounds best to you.
The advantage of setting all speakers to small is that the M60's and the amp are freed from the job of reproducing the lowest 2 octaves of bass, which are the most taxing on them. Those frequencies are instead given to the sub and it's amp, which is a specialist in reproducing those frequencies.
Mark
