Well, I heard back from Axiom and now have pricing for a new driver. In the mean time I decided to experiment. I moved not only the M3's woofer, but it's tweeter and crossover as well. Drivers from the M3 are ever so slightly larger, so the seals around the speakers are not quite perfect. The result? In a word, horrible. Detail is reduced, bass is gone. Double checked that it's not a wiring issue. It's probably due to crossover tuning. In fact it almost sound like my M3s, which never worked very well in that room. Undoing now.
Very different crossovers in the two speakers. The woofer is directly powered in the M40 (on the left), the tweeter has a resistor and two electrolytic capacitors which are not board mounted:
Can also now confirm that my M3v3 is completely veneered on the inside, almost makes it look like plywood if you don't look at the speaker cutouts!
