I'm not used to seeing "bass response" and "M2's" in the same sentence... do you have a subwoofer in the mix as well ?
I have always thought of M2's as astoundingly good speakers from 70 Hz up, but below that they don't really bother. Maybe things have changed over the years ?
I should probably go back and see if it's still true (maybe with more wattage) but other than very high volumes a pair of M2's and a big SVS sub gave the best home theater sound I have ever experienced.