Shawbrows3: yes, "trash" is very harsh. And that's how it was in my system relative to the NU's. I have started with components full of stock tubes and the designer is clearly proud of the sound in stock form. But experience already told me about the benefits of replacing certain tube types and brands. And with some effort to try a handful of tubes, the component can take on a level of performance that likely the designer never experienced.
A past L6 owner told me to listen to both of these VT-99 tube sets. He was very nice to send me the NU pair to do a compare. He said one was the Lampi tube and he said the other was the one he liked. After I listened to both, I sent him my report and he replied that his experiences matched with mine. But I don't know of the degree of the differences for me vs. him.
The focus of my system has always been to achieve decays and harmonic structures. Sacrificing things like the ultimate in resolution and bass extension were done to get the 3D magic. Bringing on the Aria preamp, Jade Ref cables and now the Lampi took the 3D to a new level and brought on many refinements previously needing much attention. And lots of effort of tube rolling throughout majorly brought on accumulative benefits. I still feel there is clarity and resolution to achieve by replacing the Sound Lab speakers' backplate components with all the latest changes. This could Be huge. And would probably show even greater tube differences.
So I'm not sure what it is about my system that makes the NU significantly outperform the Sylvania. But in my system, relative to the NU, the Sylvania is horribly flat and way too distant. Had I only had the Sylvania and this was used in a multi-DAC shoot out, I doubt I would end up picking the L6 as a top-performer relative to it's competition.