Assuming 5 is completely neutral, I'd say the Axioms are about a 6.5, maybe a tiny bit bright, but not harsh. But it's going to depend not only on which speaker you choose from the Axiom lineup, but also on your listening environment, which can have a huge impact on the perceived brightness of a speaker. My experience is with the M60's in a pretty lively room, and I've found that on certain source material I prefer to bump the treble control on my pre/pro down just a hair. But overall I would say the M60's are pretty neutral/revealing with a slightly forward soundstage.
I can't comment on the M2i's specifically since I haven't heard them, but it's my understanding that the new M2i's now use the same tweeter as the bigger Axiom speakers.
