McIntosh 501 or 602 for Magnepan 20.1

It won't be too much. It should sound a lot better with more power.
Yes, the JC-1 can run the 20.1s, but it doesn't control them the way a truly high-powered amp does. Just look at how little the JC-1s weigh. The real bruisers weigh 100-200 pounds a piece because they have big power supplies. I'm using the JC-1s on a pair of Magnepan 1.6s, where they sound much better.
Instead of getting another set of JC-1s, I'd save some money in your place and get the Classe Omicron or Omega, MK. 1. Far superior. I had them side by side. No contest.

The JC1 does have a pretty decent power supply -- the best you can get in an amp that only costs $6000/pair.

FWIW, my Magnepan dealer recommends Bryston 7B-SST for the 20.1s. The Bryston 7B weighs only 50 lbs. At least the JC1 is 64 lbs....

Of couse the Omega is better. At $25k/pair it has to be better... Why not get a pair of Simaudio Moon Rocks. They are 220 lbs each. Maybe that qualifies?

Peter

Hard to imagine going wrong with the 501's.

SimAudio W10's might work well with the 20's. They work very well with the 3.6's. Remember that the Mac's don't double into 4 ohms. I understand the power stage is looking at the fixed impedance of the Autoformers, but I tried the MC252 in my system on the 3.6's and it shut down on thermal overload after a few minutes of playing at moderate levels.
I've also driven a 600w (into 4 ohms) digital amp into clipping on the 3.6's....I'd get an amp with high current capacity into lower impedances and avoid any chance of under-powering the 20's.
Rooze

I meant Classe Omicron or Omega MK 1--they're available for 5-6,000,
On my 20.1s, I went from Omicron MK to the mono pairs you mention. Yes, the monos are better, but the originals are not that far off.