Mick,
Never heard the "KCT" or "Evolution" preamps since the upgrade. The "KRC" replaced my "KBL", and feeds an older "KSA-250". Still need to retain that amp for driving 1 ohm Apogee Scintillas. Just the idea of not having to lift my ass off the couch (remote), almost made the sale, itself!
I, too, acknowledge the dimishing return limits, but it's a constant battle fighting the upgrade temptation.
Frank