the best bang for buck, by far, is DIY.
otherwise, I would only look towards certain ID (internet direct) brands. Such as:
SVS
HSU
Outlaw
Epik
You have a large space, and trust me you need the biggest and baddest you can afford and fit. Actually make that at least two of them. Get one for now, and after you set it all up, the bug has bitten, and you can upgrade later on.
Unfortunate about your dimensions. Square is the absolute worst for acoustics. The fact that your height is also the exact same makes it truly the worst room dimensions. Hopefully your measurements are incorrect, and none of the three are indeed identical.
Just so you know, the ideal front soundstage is three identical speakers, on the same plane.
The vertical identical speaker means the true identical acoustic match.
It also means proper design for horiz dispersion in the case of multiple viewers.
the identical height means that all drivers on the same plane allow for the best panning effects possible.
however, if the horiz center is a must, then KEF makes a better design than most.