you’re using 275’s in mono? talk about way over kill. you don’t need the power of one 275 let alone two in mono. I ran LaScalas, similar enough efficiency to the Cornwall, with 2.5 wpc with out issues.
In my experience the new Cornwall’s sound fabulous on a 300b SET amp. But I have also heard them on a Class A SS amp 25wpc and they also sounded great. the SS amp gave them better bass control and top end extension but wasn’t quite as nice in the midrange but that’s what 300b’s do best.
I wound imagine the Luxman Class A amps would sound very good indeed. but stick to the lower powered class A amps you do not need the power and really lower watt amps sound better on hi efficiency speakers mostly due to lower amount of devices in the circuit. Hi powered amps just don’t’ seem to sound as good as lower powered amps with hi efficient speakers,
I second the 2A3 suggestion i also ran triode Labs 2A3's with mine. fantastic combo.