Best power amp for Quad 63

Thank you so much. You have connected a lot of dots for me. ;>)

I use McIntosh MC-60’s with my ESL-57’s and really enjoy the sound the combo produces.  My 57’s have been updated by Electrostatic Soluitions and the Amps have been updated by Yves Beauvais.

I have used many amplifiers with my Quad speakers, and owned all Quad ESL models : 57, 63, 988, 989, 2905, 2912 (as well as many other electrostatics). For 63 I would recommend Atma Sphere M-60. This is, by far, the best match for 63 model and it will outperform all amplifiers which you have listed. Stay away from Accuphase and Esoteric, as these are not realy the best choices you can do for ESL speakers. Spectral will do the job as well as ML, Krell, Plinius but you will not have with any of listed amplifiers all the beauty of sound you can have with a well made tube amplifier. Electrostatic speakers are know to work very well with tube amplifiers, and with OTL technology in particular. Some other tube amplifiers will work particularly well (for exemple EAR Yoshino V12, Air Tight models but their price is not cheaper than M-60 and OTL gear will outperform those "classic" tube amplifiers in every single aspect : transparency, bottom range, texture, natural rendition etc. If M-60 is not in your budget, try to find some other OTL amplifier, or save money and get back to M-60 later. You like Quad speakers in the first place for their utmost beauty of the middle range and transparency. In this regard matching your stats with OTL technology is the right path.

@RalphKarsten from @ Atma sphere does post here.

Kent at Electrostatic Solutions did the restoration of my 57's. 

Futterman H3 OTL if you can find one in nice shape. I believe they were also sold under the Harvard Labs brand.  These were the original Futtermans built by Julius Futterman. Wonderful synergy with older Quad Electrostatics. The H3 was also available as mono block amplifiers.

Happy 4TH of July to everyone! 😀