adding that driver makes the M50's more dynamic than the M40's. I have been told that the M50's are clearer in the midrange as well, as they have two drivers, not one, playing the midrange sounds. Bass extension is great due to the extra woofer and larger cabinet size.
Have you considered the M60's? Their midrange is more pronounced due to the introduction of a midrange driver. It is generally considered as the cleanest sounding tower speaker that most amps can drive as it is an 8ohm load, whereas the M80's at 4ohms can be tricky for most low end amps, but not Denon or Harman Kardon, to name a couple.
