Constellation makes outstanding gears. In regards to your questions on the Centaur II monoblocks vs the Centaur II 500 stereo amp, I would suggest you listen to both in the same setup.
One other alternative worth considering would be Soulution and D'Agostino Momentum gears as well as Audio Research Reference line.

Good luck

Also worth looking at the following gears for your Magico speakers : T&A, Tidal, Ayon, MBL, Devialet, Lamm.

I would highly recommend the D'Agostino Momentum & Progression series, Soulution, Tidal, MBL, Pass Labs, Classe Delta CAM600, CAM300, McIntosh Mc601, MC301, MC452, Simaudio Evolution series amps, Audionet, PS Audio BHK monoblocks, etc etc etc.