* UPDATE * Put in Fivre 6N7GT - these had very little play time so far - and they distort. So you are right guys - it's the 6N7G tube itself that needs the burn in. Come to think of it - I used the Visseaux's with EL3N for a while because that did work without distortion from the start. Those hours with EL3N of course helped the burn in of the Visseaux! So it makes sense it 'suddenly' works with 5998 too. The whole experiments to me is proof that tube burn in is VERY real. Not just to cure pops etc, but also to bring a tube 'on spec'. There are many disbelievers of burn in with respect to sound quality, including that of tubes. Guess with a tube run at it's optimal operating points, it's hard to discern a burn in effect but with these Visseaux in Elise, it seems very easy.
Whatever, I'm relieved the joybringers now work. I truly feel like a lucky one
I recognize the forward character but it's funky and makes the non-audiophile stuff sound like magic. Next to try: FDD20! Hope to make the adapters today.
Thanks to all of you pioneers who brought all these nice tube to our attention.