A thought about your "EDIT", when in "Double Bass" mode, a setting of 100 Hz for the crossover makes the sub pick up the 100 Hz info in addition to the M60s. So the M60s are going as low as they can, and the 8" sub is starting at 100 Hz.

Pioneer PDP-5020FD, Marantz SR6011
Axiom M5HP, VP160HP, QS8
Sony PS4, surround backs
-Chris