Slo, as Rick pointed out, the anechoic frequency response curve isn't accurate below 90Hz or so. I can assure you that in my room the M22s exhibit no "hole" in the 80-100Hz area, and with room reinforcement have good response down to about 50Hz.
This is in accord with the enclosure tuning, which the low point in the impedance curve(
NRC graph )indicates is around 55Hz.
The effect that you describe may well be due to speaker placement and wouldn't be improved with the M50s. Further experimentation with placement may be useful, and in particular you should be careful to have the centers of the mid/woofer cones at unequal distances from the floor and two nearest walls.
The possible room effect that I mentioned wouldn't be due to standing waves, but rather sound reflections from nearby room surfaces causing peaks and valleys.
