The Valve Art KT-66 I tried was more harsh than the 6L6s I’ve tried.
I spoke to Bob Pletka at Eurotubes about it (he has always given me good advice), he said the Valve Art offering is not a good representation of what a KT-66 should sound like, so I guess I’ll have to try another.
I tried the JJ E34L, JJ 6L6 (and various others) and a JJ 6V6. My fav is a good 6L6 so far. I’m using NOS 12AX7s and 5Y3 (Sylvania) tubes, the NOS rectifier makes a big difference over a modern version of a 5Y3.