It's loud, but not as loud as a 300
lb sub should be.

Are you sure you heard it driven with enough power? I just reread the
specifications on this thing and it says 6,000 watts RMS, 12,000 watts peak.
The amount of current required to achieve this kind of wattage (ON A
CONTINUOUS BASIS!) would be massive. A couple of 1500 watt class D amps
just wouldn't cut it. Sure, SPL vehicles routinely spit-out this much
power, but it is always for very brief bursts. I have to imagine that if
you COULD find an amp or amps to provide this much power (and then a way to
supply these amps with a CONTINUOUS supply of the 1000's of amperes needed),
it probably would be pretty damn impressive!

But, of course, what I just said really defines the problem with a subwoofer
like this. It is certainly a technological marvel, but it seems nearly
impossible to fully utilize it in an autosound environment.

MOSFET