Why don't you go all the way and make Transmission line subwofers, like TLS Guy.... these are huuuuuuuge, and a Maelstrom-X based TL sub will be big.... but probably quite hard to beat....
Well, according to TLS, you need two drivers in each sub to make his tuning work properly
And a good thing, it's impossible to steal, once in place noone is going to be able to move it anywhere
if tuned at 17Hz, they'll probably have useful in-room response down below 12 Hz, yes?
Matt, you have room for these, yes?