Just my two cents...I have tried both the Furutech and Hi Fi Tuning Supreme fuses in my Modwright preamp. And yes, I have been able to hear a positive sonic improvement. I can relate to the naysayers and skeptics when it comes to the multitude of tweaks out there...some with outrageous claims and "voodoo" science, but these seem to "work".
I originally tried the Furutech after reading a recommendation by Steve McCormack ( who does know a bit about audio
) and who is someone that I trust, having had some personal communication with him when I owned one of his amps. The cost for the fuse was not prohibitive if it made a positive difference, and I tried to be aware of any potential bias on my part.
Anyway, in my system, I liked the result...and I only wish that I was comfortable enough to open up some of my other equipment to replace the stock fuses in them.