It's the first time I write on this forum.
I don't know If you've still have your problem, I had the exact same problem with my new M22 (2 weeks old V2 box with V3 speaker)running with a Pionner Elite 7.1 VSX-919AH-K , 120 watts per channel. I did all what you do to correct the problem and when I try my amp with my old Bose (23 years), my amps runs without problem until +.. DB.
I finally discover that the problem was one of the M22, both woofer was dead, I return it to Axiom and they send me a new one ( all V3) last week, for moment all is OK, i pushed my amp until -10 DB and it's OK for the moment and I'll go harder later.
So check if you've got sound on all your speaker by playing them one by one.