I hadn't followed up my earlier post with the Super's in the Focal's. mg8's comments capture what I hear, although I find them a touch dry (improved with aging) and voices a bit recessed vs. the stock fuse, neither of which I prefer. The effect of the change was, absolutely speaking, the greatest I'd experienced, with Acme or either HFT version on other components (don't have the HFT Supreme anymore to compare).
Someone wondered how or why fuses make a difference. The way I see it is they are in the electrical power path, so it's as if one were changing a very short power cord. However, for an engineer, or least some, there are limits to what such a change can do, for example, not tonality. Here's an explanation I received the other day from one who makes excellent cables, amplifiers and speakers (and power cords on special order):
"Power cables do not transfer the music signal, like interconnects or speaker cables, so they do not (can not) change 'tonality'. What they are supposed to do (primarily) is transfer power to your electronics, power amp especially, without constraints. That's why we make them with solid, thick, pure copper wires like described below. What's the effect on sound? The primary effect you should experience is improved sound 'solidity' and better defined (more solid) bass. Also, you may notice a cleaner ('blacker') background and less noise due to shielding. That may be more or less noticeable depending on how 'noisy' is your environment."
When I replied that theory aside, as a listener I hear tonality differences between cords, typically within the first hour of burnin, and moreover some small cable companies explicitly advertise tonality differences, even to order, he replied:
"True, all cables make some difference that can be perceived by a listener one or another way since we all hear differently. I have no doubts that you experienced that difference the way you described it. The comments in the message were from a designer and an engineer point of view. Sadly, this industry tends to overhype, overpromise, and exaggerate as a part of various companies marketing campaigns. Interestingly enough, more overhype is usually linked to less science and an indicator of what a specific company stands for. So, it shouldn't be taken for granted. Sad reality."
Theory aside, I still hear tonal differences and still see professional reviewers speaking about them. I also picked up a tonal difference between the Acme vs. HFT Supreme in a pair of Emotiva airmotiv4 speakers, the former being a bit darker (and not quite as clear).