Interesting. I've never heard the M106, but I bought the M105 over it due to the superior spin. Seems kinda normal in the industry that the cheaper and smaller models often measure better than their bigger and more expensive brethren. Examples include M105 > M106, Genelec 8351b > 8361a, JBL 705 > 708, JBL HDI 1600 > 3600. Often times the bigger models are way more expensive, too(like 2x). For twice the price, you get a little more max output, a little more extension, and a little worse sound.
It just seems like it's easier to integrate a smaller driver with a tweeter. The F208 has some of the best spins in the group, for instance. Interestingly, i know the M106 has similar (and maybe better) spins than the M16, but I strongly preferred the M16. Voicing still counts. The M105 had the most neutral treble i've ever heard, but didn't do well in the large-ish room i was auditioning in (with the clerk standing over my back making sure i wasn't going to blow their speakers). It would probably kill in a real room, especially with a subwoofer. How do you like yours?
I wonder if i need to build a pair of Philharmonic BMRs for "science."