I went from Pass to Coda to Parasound and finally settled on the original Parasound A21 (better than A21+ BTW) as my preferred amp for my separates (I actually prefer a Yamaha integrated to all of them but that’s largely a speaker synergy thing).
The Pass I owned was the XA25. A very nice sounding amp but simply didn’t have enough juice for my stable of speakers.
Subsequent to the XA25, I tried the Coda No.8 V1. It’s also a nice amp—very quiet and resolving and a little all around superior to the XA25. It would’ve been perfect had it been able to give me the same “effortless” presentation the Parasound does.
The Parasound is the warmest of those 3, but still decently resolving and sounds the least taxed at spirited volumes. Pairing the original A21 with a highly transparent preamp and source goes a long way in offsetting its otherwise dark character.
If the JC5 merely sounds like a better A21 (though it is arguably inferior in bench tests), then I think it would be an excellent choice if the other sides of your chain are highly resolving, which your speakers are IME.
I haven’t heard the MC312 specifically, but if it sounds similar to other modern MACs, I would save some cash and simply opt for the JC5.
Perhaps a better option would be to get a Levinson amp to pair with your preamp and keep it in the Harman family.