?Best speakers for a 2000 sq.ft loft?

Your M-Ls should work fine as long as you sit in the near field. Place the speakers in the free field (a good thing) and seat yourself near a wall (for bass reinforcement). There's no need to pressurize the entire room.

the new b&w 800 seires will work well because they love an open area as such. Good Luck Gino

I saw an ad for the Genesis 201's here yesterday for less than half price. These are 4 towers w/multiple driver arrays. Two of the towers are bass/subwoofers, and the other two are tweeters and midrange. this is an incredibly good-sounding system, it blew me away, though I ended up with the Genesis 500's because I didn't have near enough room for the 201 system. If you've got $10,000, you should try to hear them.

If you want to stay with Martin Logan, a pair of Prodigy can fill up a 35'x60' room very nicely.

The original B&W800's, preferably actively bi-amped. This speaker is truly a bargain, even at its original price, and a downright steal on the used market. It can be first run normally and as finances permit, bi-amp actively.
This speaker can produce 120 db at 4 meters easily (with the delicacy you are use to with the M-L's.)
It will fill your room and then some.
Richard