I've been checking out the THD (distortion) measurements of a number of speakers including all of the axioms.

http://www.soundstagemagazine.com/speakermeasurements/

It looks like the best measurements in the axiom family went to the m80 and m22 given that they had low distortion throughout the frequency range. The m2 and m3 did not do as well and most of their distortion was in the bass octaves.
Is this why people prefer the m22 to the m2 and m3? Is this distortion an audible problem?