Hi_hifi, I'll try to offer a little advice and encouragement on your intended system, since I own Sound Lab U-1s and am a Sound Lab dealer located in the Chicago area.
First of all, hats off to you on an excellent choice of speakers! (grains of salt all around) In your room either speaker would work. M-2s are easier to drive than M-3s, and it's unlikely you'll be wanting for bass augmentation especially if you go with the M-3s. One person I know has Auras (which use similar size panels as M-3s) supplemented by a subwoofer in a room about the size of yours, although a pair of Sound Lab U-2s (same size panels) in an 11'x12' room about 2 1/2 to 3 feet out from the corners sounded quite good as well as in a slightly larger room. Although the frequency response specifications for both the M-2 and M-3 are similar enough, in-room response is different depending upon natural room reinforcement, which in turn depends upon the room size and acoustics. Another thing to consider is the horizontal radiation pattern, 60 degrees on the M-3 vs. 75 degrees on the M-2. The M-2 may prove to be more tonally rich and full bodied than the M-3, to an extent determined by the room. In your room I think you'd hear it. At the same time it's good to have room for the speakers to breathe, and in smaller rooms the smaller speakers may image better.
As for amplifier choices, I have experience with Atma-Sphere MA-1s driving my U-1s. Especially on the current production speakers which enjoy a significant efficiency improvement, the MA-1s should easily be able to drive either the M-2s or M-3s well. Zero autoformers may be worth considering to raise the effective impedance, especially if you go with M-3s, although one of my customers didn't like the Zeros with his M-2s and MA-1s, finding them veiled. I can't speak about how well ARC amps match up with the current production Sound Labs, but only the REF models, especially the REF600s (one of my customers uses them to drive his U-1s), were capable of driving Sound Labs satisfyingly until recently. The VT200 and VT100 now may be capable of driving them. The bigger VTLs seem to be a good match, as Albert Porter reports that his VTL 750s drive his U-1s quite well, so the 450s may be worth checking out and ought to be tons of power for the newer production Sound Labs.
If you're in or plan to visit the Chicago area sometime and would like to come for a listen, including some of the above amplifier choices and perhaps others, let me know and be my guest. Meanwhile, feel free to pick my brain for what little is there. Always glad to help. Best of luck!
Brian
First of all, hats off to you on an excellent choice of speakers! (grains of salt all around) In your room either speaker would work. M-2s are easier to drive than M-3s, and it's unlikely you'll be wanting for bass augmentation especially if you go with the M-3s. One person I know has Auras (which use similar size panels as M-3s) supplemented by a subwoofer in a room about the size of yours, although a pair of Sound Lab U-2s (same size panels) in an 11'x12' room about 2 1/2 to 3 feet out from the corners sounded quite good as well as in a slightly larger room. Although the frequency response specifications for both the M-2 and M-3 are similar enough, in-room response is different depending upon natural room reinforcement, which in turn depends upon the room size and acoustics. Another thing to consider is the horizontal radiation pattern, 60 degrees on the M-3 vs. 75 degrees on the M-2. The M-2 may prove to be more tonally rich and full bodied than the M-3, to an extent determined by the room. In your room I think you'd hear it. At the same time it's good to have room for the speakers to breathe, and in smaller rooms the smaller speakers may image better.
As for amplifier choices, I have experience with Atma-Sphere MA-1s driving my U-1s. Especially on the current production speakers which enjoy a significant efficiency improvement, the MA-1s should easily be able to drive either the M-2s or M-3s well. Zero autoformers may be worth considering to raise the effective impedance, especially if you go with M-3s, although one of my customers didn't like the Zeros with his M-2s and MA-1s, finding them veiled. I can't speak about how well ARC amps match up with the current production Sound Labs, but only the REF models, especially the REF600s (one of my customers uses them to drive his U-1s), were capable of driving Sound Labs satisfyingly until recently. The VT200 and VT100 now may be capable of driving them. The bigger VTLs seem to be a good match, as Albert Porter reports that his VTL 750s drive his U-1s quite well, so the 450s may be worth checking out and ought to be tons of power for the newer production Sound Labs.
If you're in or plan to visit the Chicago area sometime and would like to come for a listen, including some of the above amplifier choices and perhaps others, let me know and be my guest. Meanwhile, feel free to pick my brain for what little is there. Always glad to help. Best of luck!
Brian