The Tenor will work fine with the ESL63s insofar as power is concerned. The ESL 57s will be over-powered and the potential for damage is high if a tube fails. For the the newer Quad designs, you will have enough power but will find the ZEROs handy as the newer designs have low impedances since Quad is trying make the speaker more compatible with transistors. Despite that they still sound better with tubes.
ESLs in general can be damaged by arc-over events in 6C33 power tubes. It is this arc-over issue (as well as a limited service life of the tube sockets) that kept us from extensive use of the 6C33 in our own designs, and why you are getting some reluctance from Tenor. I would consider placing an in-line fuse in the speaker circuit to prevent damage if a tube arcs. I would set the value at 2.5 Amps and see how that works- you might have to go up to 3 amps but I would not go above that. That way the fuse will blow if the output power of the amp is exceeded, which can happen during an arc-over event.
ESLs in general can be damaged by arc-over events in 6C33 power tubes. It is this arc-over issue (as well as a limited service life of the tube sockets) that kept us from extensive use of the 6C33 in our own designs, and why you are getting some reluctance from Tenor. I would consider placing an in-line fuse in the speaker circuit to prevent damage if a tube arcs. I would set the value at 2.5 Amps and see how that works- you might have to go up to 3 amps but I would not go above that. That way the fuse will blow if the output power of the amp is exceeded, which can happen during an arc-over event.