I have them set up with a BSS London outboard DSP XO so will try some different amps. The challenge is you need 4 identical channels of sufficient power for ease of set up. The Crown DCI definitely does that job well, but the fans are just too obtrusive for my home environment.
But what is sufficient power, really? The 1200W power requirement is to meet the M2's 123dB SPL and distortion specs with Crown amps. 1200W@ 123dB means ~5W @100dB. And that makes sense because the M2 woofer's sensitivity (2216Nd) is 95dB@1W/8R, typical of most 15" professional drivers. Audiophiles use drivers with high sensitivity like that for their 2W SET amps. The M2's 1200W@123dB spec leaves good headroom, and at 100dB the 2216Nd actually burns only 3.5W. The D2 has a passive attenuation network and even higher sensitivity than 2216Nd. At 105dB, as loud as I would ever play at home, M2 needs <10wpc x2.
Modulus 286 is 2x40wpc @8R. That should make >113dB, w/ two M2s playing in-room at clipping. But mod86 distortion stays low to full power so >107dB is realistically usable SPL. Mod86 SQ is generally well regarded, I think you'd be pleasantly surprised if you haven't heard this little amp yet. Electrical damping is comparable to DCI, as both use abundant negative feedback. Mod86 is at least as resolving as DCI, imo. It's shocking the resolution the first time you hear it.
I use single channel Mod86 on my 92dB sensitvity, 4ohm (2.9ohm dips,) passive xo, 4 way Legacys in a very large room. It plays very loud and sounds excellent. Mod86's 65w@4R is not quite enough for the full performance envelope of the Legacys, so I occasionally get a trace of thermal protection when I really push it hard. But that is a far bigger load than a single active 15" 8ohm 95dB woofer which would voltage clip before thermal protect.
I have 4ch of Mod86 (ver1) that I can put into a box for you guys to try with the M2s: Jason, Tom, Joel, if anyone's interested. I have Par86 I plan to build for the Legacys anyway, and extra chassis and tranny, etc. Eventually I'll make 2 3way mod86 amps for future speaker projects, but not planning to use them anytime soon. I personally would love to hear Mod86 on M2. But you need external crossover - Mod86 don't do no math.