The M22 is 3db more sensitive then the M2 ... so I'd go that route over making an M2 active (factoring in the $)
We assume that everyone knows what the sensitivity spec means (which may not be as useful as you would think as I will discuss below). To keep it simple a speaker which is 3db more sensitive then another will need 1/2 the power to play just as loud. So a M22 with 50Watt amp will preform equivalently to an M2 with a 100Watt amp.
When combined with a decent sub , the sensitivity and the linearity of the M22 makes it one of the best options in the Axiom space for receivers
Now, for comparing SPL numbers ... I'm ok with comparing the SPL specs of the M2 and M22 because they are spec'ed by the same manufacture (measured in the same way) for the same frequency range.
To compare the M2/M22 sensitivity to other speakers in the line up you need to understand how it was measured. One may note that the M5 and the floor standing models claim that they are just or even more sensitive as the M22 ... this might be misleading as it can measured at just one frequency (some manufactures might measure it at the speakers most sensitive frequency), or a average of many frequencies or with pink or white noise. Changing how you measure it will effect the numbers. So you might not be comparing apples to apples. As far as Axiom is concerned ... I have no doubt that we can compare these speakers to the M22 if we stayed in the M22's frequency range ... But, I guarantee you the the low-end on the floor standing models will increase the power needs by quite a bit. I.E. you may find that you start clipping at way lower volumes playing an M100 (spec'ed @89db) then the M22 (spec'ed @88db) on your average receiver.
