KEF R11 would sound the best with McIntosh amplification. I have suggested this to others who had bad synergy with a variety of other amps including Parasound and they were quite pleased with the Mac.
The pass XA25 sounds different than their up range amps which tend to extend the treble more despite being class A. To my ears the new KEF R series require an amplifier with ultra smooth top end. The JC5 is probably better in that regard than the up range Pass.