?Best speakers for a 2000 sq.ft loft?

Whatever you get they will obviously need to be on the high-side of sensitivity. Consider horns, the Avantgardes perhaps?

I agree, your SL3's will get lost. At the kind of distances involved in a 2000 square foot room, hybrids are out. This is because the panel will approximate a line souce while the woofer acts as a point source, and sound pressure level will fall off more rapidly with distance for the woofer than for the panel. So the SL3's will sound thin and weak in that room.

I have no idea what your budget is, and unfortunately that's a significant part of the equation. Also, what are the acoustics like - is the room echo-y? I'd hate to think what it would cost to acoustically treat a room that size, so we'd need a speaker that would work well with what you've got.

The ideal speaker would have good timbre, high efficiency, and a well-controlled radiation pattern. That big room could end up being a marvellous blessing or a hideous curse, and it will largely depend on the choice of speakers.

Also, can you describe the place in more detail? I'm not entirely sure that what I picture in my mind when I hear the word "loft" is necessarily what you intend.

I realize I haven't answered your question at all. Sorry, but I don't have enough information to get started yet.

Best wishes!

anything really huge Pipedreams, Genesis 1's or similar, that's alot of air to be moving your going to need alot of power also suggest VTL Wotan 1200 amplifiers.

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.