I have a similar take to yours on the EH vs. SED versions of the KT88 as for how they sound, but a diametrically opposed opinion on which I prefer. I enjoy the clarity and speed of the EH, and didn't really care for the warmer SED (I prefer their 6550C more in my VTLs as a viable compromise, and admire their EL34 too).
I'd also found the Chinese 'Ruby' 6SN7 to be a very competent driver in a CJ amp, close to the same ballpark as some NOS American versions (something I couldn't say about the Sovtek). But of course we all have different systems and tastes, glad you've identified something for yours.
I've generally found that power tubes take a couple days' worth of *playing time* to open up and flow, which for most people means a week or two. And whenever I've had incipient problems with glare, it's always turned out to be traceable to microphony of the input tubes; other than trying to get the best-sounding and least-microphonic NOS examples you can, I would also recommend trying some type of tube dampers here to help tame glare.
Once you get all that squared away and if you still have them hanging around, you may want to revisit the KT88EH's after a while, let them finish burning-in and see what you think again. They will always sound leaner and less 'tubey' in comparison with the SEDs (to me they're more neutral), but I feel they hold a few other advantages in fidelity, provided the tonal balance can work with the rest of your system. (BTW, if you -- or anybody -- is in the market for a spare matched-pair of little-used SED KT88's, email me.)
I'd also found the Chinese 'Ruby' 6SN7 to be a very competent driver in a CJ amp, close to the same ballpark as some NOS American versions (something I couldn't say about the Sovtek). But of course we all have different systems and tastes, glad you've identified something for yours.
I've generally found that power tubes take a couple days' worth of *playing time* to open up and flow, which for most people means a week or two. And whenever I've had incipient problems with glare, it's always turned out to be traceable to microphony of the input tubes; other than trying to get the best-sounding and least-microphonic NOS examples you can, I would also recommend trying some type of tube dampers here to help tame glare.
Once you get all that squared away and if you still have them hanging around, you may want to revisit the KT88EH's after a while, let them finish burning-in and see what you think again. They will always sound leaner and less 'tubey' in comparison with the SEDs (to me they're more neutral), but I feel they hold a few other advantages in fidelity, provided the tonal balance can work with the rest of your system. (BTW, if you -- or anybody -- is in the market for a spare matched-pair of little-used SED KT88's, email me.)