It may be that the volume knob on the subwoofer is not turned up all the way so no matter how strong a signal the receiver is sending it volume level set on it’s internal amp is limiting the spl. I’m assuming here that it’s a powered subwoofer.

It may also be that the M60s are “corner loaded” and receiving a bass boost from room reinforcement.

Just a couple possibilities,

Dean

P.S. Still it’s a nice demonstration how powerful Axiom speakers are.

3M80 2M22 6QS8 2M2 1EP500 Sony BDP-S590 Panny-7000 Onkyo-3007 Carada-134 Xbox Buttkicker AS-EQ1