I will chime in as a former owner of the Magnepan Tympani 1D speakers (which I think were the immediate predecessors of your speakers).
The good news is that because the bass panels are well damped mechanically and the impedance is (claimed by Magnepan to be) "purely resistive, 5 ohms at any frequency," amplifier damping factor should not be an issue. So you can use tubes or McIntosh autoformer amps without damping factor issues.
I am surprised that you did not like the MC2100. I want to amplify some of what was said above to say that unless the C26, C32, MC240, MC2100 have all been properly restored (re-capped and with other components replaced as needed, cleaned and bench tested, your listening impressions my not be useful or correct because the equipment may not be working to spec. E.g., you may not like the sound of the MC2100 because it may not be working to spec. When I bought my MC2505 (very similar design to the MC2100), it sounded old, fuzzy and funky. Upon return from restoration by Terry DeWick, it not sounded like one of the sweetest most musical amplifiers I've owned (over the last 45 years). So make sure everything is up to snuff before making listening comparisons and decisions.
I also have a MC275 IV (relatively modern version) which sounds more solid state-like but retains the open, clear midrange that I like with tubes. But not sure how it would sound on you Maggies.
A couple suggestions:
1. An older (totally restored) Audio Research D76A might be a cool amp for your speakers. Recall that the early days, Magnepan was helped along by ARC so you may find some (deliberate design) synergy between your older Maggies and older ARC amps. I recall hearing that Amp along with an ARC SP1A preamp and a pair of Tympani 1C speakers and it provided really beautiful, lushes mid range sound. It really left and impression but that was a long time and my memory may not be perfect.
But having said that, I found that my restored MC2505 (and my MC275) are both be sonically superior to my prior ARC D115 MK II amplifier, so unless there is some magic synergy, I would stick with Mc.
2. I think a better suggestion is bi-amplification - which is what I did with my Tympani ID. Your speakers are specifically designed for this and the
owner's manual provides a lot of info on how to bi-amp. The down-side is that Bi-amping requires adding a crossover network between the pre-amp and the two amplifiers and (my old experience / experiments with the Tympani's) informs me that the an active cross-over network can add noise and distortion and may not be up to par with the surrounding Mc equipment. The good news is that the Maggies have a simple crossover design and are relatively easy to bi-amp. And the operator's manual
addresses this issue (on pages 5 & 6) with suggestions on how to provide a minimally intrusive crossover network.
If you bi-amp, you could, for example, keep your (fully restored), sweet sounding MC240 connected to the tweeters (which will demand far less power from the MC240) and use maybe a pair of modern MC275 amps in mono-mode to put 150+ Watts into the bass panels and still have similar tube sound from the MC240 and MC275s through the midrange. Or something like that.
Good luck. Have fun.