I remember the first time I heard the improvements brought by an upgraded fuse. It was a few years ago and our German distributor, Jurgen, was visiting. We were in the middle of a listening session and he asked if I might be up for an experiment. Of course! He pulled the top off the DirectStream DAC and took control of the listening session.
I was told only that we're now listening to A and then B (and so forth). I hadn't a clue what he was doing nor which was A or B. The difference between the two was rather remarkable. If memory serves the upgraded fuse he was pulling in and out was from Audio Tuning.
I was dumbfounded by the level of improvement from replacing that fuse. Hell, I was dumbfounded that a fuse could even make a difference, let alone that much.
That experience led us to start paying attention to the fuses our purchasing department acquired and, eventually, to spec only specific types for our products. Like we do for other passive components like resistors and capacitors.
What we ship with our products are excellent sounding fuses (though not expensive aftermarket types). Can one do better? I am certain there will be those that believe this to be true (and it probably is).
However, there comes a point where spending hundreds of dollars on a component whose sole purpose is to give its life might just be a questionable practice.
What happens if it does its job?
There just might be more practical means of making improvements in sound quality.