Stephane, the M2s do in fact have less bass, both real and perceived, than the M3s. The NRC lab impedance graphs clearly show that of the Axiom bookshelves the M22s have the lowest bass tuning, followed closely by the M3s and then a somewhat wider gap to the M2s. In addition, the M3s have a small upper-bass hump which both makes fundamentals in that region more prominent and gives an impression of lower extension by making the harmonics of low bass notes louder.
The best way to see if you could "live with" the M2s is of course to try them. Some members here, including John Bridgman and Robb(Hutzal), have some experience with both and may be able to add their thoughts.
