slack,
You've already answered your questions by yourself.
Most importantly, rely on your own ears since you are lucky enough to have a chance to audition both speakers. Since you will already cover the most relevant factor (which is your own listening tests), I just wanted to link to some NRC measurements available at
audiovideoreviews.com.
M3 frequency response (listening window, +/- 15 degrees off-axis averaged):
M22 frequency response (listening window, +/- 15 degrees off-axis averaged):
As you see in the graphs, the "real" bass extension is almost identical in these speakers. However, the M3 has a significant hump in the 80-200Hz region, which may provide a subjective impression of "more bass" for some listeners. Also, the M3 exhibits a broad dip in the 1.5-10kHz region (especially 3-8kHz), which may explain many people's impressions that these speakers are more recessed, laid-back, relaxed and mellow. In contrast, the M22 shows a definitely flatter response above 80Hz, consistent with its impression of an accurate, more detailed sound.
If it were me, I would likely go with the M22, which I know blends with a subwoofer seamlessly.
