Passive subwoofer amps help!

I acquired two massive subwoofers (over 230lbs each) that were mated to a $100k+ custom system and I need to power them somehow. In my limited research, I'm a bit confused about all this.  I'm used to my subs being powered.  The subwoofer amps I've found by Dayton Audio seem to be very lower powered.  Can I just buy an SVS PB16 amps off ebay and build a box and use that? That gives plenty of subwoofer power and the ability to control with phone. Or is that a big sin in the subwoofer world?  Why are there not more external high powered solutions for this with a volume knob, low pass knob, and phase switch on the front. 

I did look at the Klipsch RSA-500 but it specifically lists the subs this amp is to be used with.  Also, for $1k+, it's not that powerful.