I can't speak to much to all the great sounding experience/options in the above posts but I just finished and installed my BFM THT-LP, 15" sub with a BASH 300,
in my 900 ft3 man cave and all I can say is Wow Wow Wow.
If I had the budget you do, I'd build 2 15" daayton speaker powered THT's and get the mini-dsp for a room your size and have money left over for an REW experience dialing it in..
The plans work.
The support from the on line community will not let you fail.
As I did not have to deal with a WAF the lp version fit in all locations as REW may best help me determine.
My build pictures are at williamtomkiel.imgur.com,
I had a lot of fun doing the homework and "visualizing" the dry fitting and clamping and on and on.
And the opening battle scene on the BD LOTR when Saueron (?) goes "nuclear" that sound in HUGE, LOW, LOUD, GRITTY, GRINDING and rattles the seats.
I'm pretty sure that's your goal.
The right thing, once, the first time.