HI,
thanks for all your suggestions and answers.

Fisrt, I don't have dual post on my M80. Are they supposed to all have dual post ?

I've check my phasing with the battery test and everything is on phase.

I've also looked at any configuration regarding the Impedance of the speaker in the Amp and found nothing.

My Home Theater is in my basement. Floor is made of Cork tiles and my ceiling is made with acoustical tiles.
it is apprximatly 22' wide x 18' long (but not square).