The American made 6sn7 VT-231 (as opposed to the GT or GTB) from the early 40s is the best sounding 6sn7 ever produced. The Kenrad and Sylvania are two of the best VT-231. Beware that the Sylvania is prone to microphonics however. I don't know what your room sounds like, but based on your system, I would recommend the Kenrad.
BTW, congratulations on the ESL amp purchase!
BTW, congratulations on the ESL amp purchase!