which is why I recommended the SPLaudio customs. just tell him your intentions (power, box size, goals) and he'll make the right setup for you. Also with your space, you could look into a single 15.
I've heard the Fi Qs like alot of space as well (minimum for the 12 is 1.8cu ported). I even had an 18" Fi Q sealed in about 4-4.5 cubes (the minimum requirements on their site at the time) and it was decent but i could tell it could do more. I've heard good things about DC subs in minimum space boxes though. At any rate, with 3 cubes and 2kwrms, I'd look at the DC lines or a custom sub (if you really wanna do 2 12s). I could be missing something though.