Kharma Ceramic 1.0 speaker with Atma Sphere Amps ?

This thread begs the question of why Ralph Karsten, who was one of the first to use the 6C33C in any configuration, let alone OTL, that I can remember, stopped making those models to go with the 6AS7 exclusively in his Atma-Sphere OTL amps. He must have had his reasons, but the tube seems to have taken off since then - first Joule-Electra, then Lamm, Tenor, etc. Just curious; I've never heard any of these!