As far as I am informed, EL34s are not the way to go. KT90s will work, as well as the types you've mentioned.
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I'm not as familiar with the recent marks of this amp, but the French Jadis website says that it was originally designed for use with EL-34s, but the 6550s, even plain old GEs, sounded better. I would think you'd have to have someone change the internal bias if you want to do this, as the Defys weren't self-biasing like the JA 30s, 80s and 200s. Finally, in my view the Defy was always tubby and over-ripe in the bass, even with 6550s; I would expect the performance in that area with EL-34s to be even worse, although the midrange should be better. If you don't run it full-range, that might not be a problem.
You should send an e - mail to Jadis.
In my queries to Jadis, they have only recommended two tubes to me(for several of their products). EL34/6CA7/E34L or KT90. They have told me the sound of 6550s is not as good, and their experience with KT88s have been horrific. Jadis used to be a proponent of 6550s before switching their allegiance to KT90s.
My feeling is that EL34s would be OK. Especially, if you like the sound(and that's what the picture showed). I presume the Defy 7 is autobias. As far as I know, the only Jadis amps which are not autobias are the Orchestra and Orchestra Reference, and they are perhaps the most difficult of tube amps to bias.