Charles, everyone reading this thread knows you replaced a Solen with a Duelund CAST and noticed a big improvement. That's great and I am glad you're happy, but it's hardly surprising. Solens are, to put it politely, not a very high threshold to surpass. Here's an analogy: if someone replaces the Pioneer transistor amp he's been using for the past 20 years with an Audio Research preamp and amp, he will be very pleased with the improvement. That doesn't mean, however, that ARC is the best sounding amp in the world. Without hearing other high-quality amps, he may be quite happy, but if he hears VTL, VAC, Emotive Audio, CJ etc., he will realize that the ARC equipment has flaws and he may prefer another brand instead.
It's the same thing with capacitors. You need to try a lot of different caps and in various applications to gain a full appreciation of each cap's sonic qualities. A few months ago I posted something in this thread asking people to describe any negative qualities they hear in CAST caps. As I recall, Grannyring and I were the only ones who had any complaints. That's not because we have super-human hearing. It's because we have spent a lot of time comparing different caps.
And that is why I say in order to gain a more complete, a more nuanced understanding of what a cap sounds like, you have to compare it to other caps of similar quality. That hardly seems like a controversial statement.