The Mephisto Stereo is 50k Euro in Europe and has a quoted input impedance of 20kOhm, the minimum required by ARC as you know. Can you get it for under 50k $US?
I couldn't find the input impedance of the Momentums.
The Accuphase is certainly warmer than Moon but I don't think it has the same speed/slam, it's a more relaxed presentation.
I suggested the MX-R because of the very high input impedance, but if you're looking for added warmth I don't know if it will satisfy you. Giving it a try won't hurt I guess.
The MF Titan is warmer than the Moon; this particular model is made in the UK; as far as I know just the lower end stuff is made in Taiwan.
I find that the Moon line from Simaudio is warmer than the Evo line. You should try the 400M monos as a cheap alternative, I think they're a bargain at their price. There's a pretty accurate review of them on Soundstage.
Simaudio Moon 400M Mono Amplifiers