The proper way to approach this is to give some thought as to what amplifier would be a good match for your speakers. Will the amplifier meet the demands of the speaker and if so, will the synergy be a favorable one?
Preamplifier should then be installed in the audio chain so that the differences will be more easily appreciated and evaluated for the characteristics you desire. More transparency, detail, soundstage width and depth, more focus with increased palpability factor, liquid, smooth and musical presentation, etc.... Throwing money at one or the other and approaching it that way may or may not put you in the ballpark since a great preamplifer will be masked by an amplifier that is either not synergistic with your speakers or does not properly drive the speakers.
Having said that, your ML speakers are of fairly sensitive 90dB efficiency and although the impedance does drop rather low and especially at the upper end, where it falls below 1 ohm, any of the McIntosh amps you have mentioned will get the job done. The synergy is a different question and it is mostly a personal preference as long as the amplifier is handling the speakers properly.
Having lived with ML electrostatic speakers in the past for quite some time and experimenting with various gear, given ML's revealing and rather non-forgiving nature of anything upstream that is not up to par, I'd shoot for an amplifier that does not have a tendency of sounding lean as the presentation can be relentless and fatiguing. Once again McIntosh should be a wise choice here as typically and if anything, McIntosh amps will tend to err on the weightier and meatier if not ultimately resolving presentation which would be a plus in my book.
I'd be tempted to try a top notch McIntosh integrated with those speakers if I was in your position. Tubes in a preamplifier can be a hit or a miss when it comes to very revealing speakers and unless you are willing to tube roll to find that balance, the integrated should be a good pairing in my mind.
Good luck with your quest.