@Reinhardt The frequency control is for the low pass filter and should be set to 80 or so. It will only allow frequencies that are under where it is set to be played. Typically you want the subwoofer to only play from 25ish to 80 or so but varies based on setup, woofers, box, music type, etc.
I would hook-up the kicker and turn off the bass boost and do a comparison. Also set the gain with a DMM and play the same tracks. having bass boost set can and most likely will damage the subwoofer over time, how long depends on how bad its clipping. An easy way to see what's going on is to hook-up the amp, set the gain with a dmm, then turn up the bass boost and see what happens on the DMM. I have had amps go from 40v to 70s by adjusting the bass boost.
Whoever said that MMAT's was underrated because they used smaller fusing needs to do some research.