I tried one HiFi Tuning Supreme fuse in my Classe Audio SSP-800 to see what all the fuss is about and I have to say I can hear a difference. More opened and detailed. Then I tried swapping direction of said fuse and, again, there was an audible difference. Weird. Both ways are good but one centers the image more and the other way gives a perceived wider soundstage. I did this several times and it was pretty consistent.
I was so impressed I ordered more fuses for 3 of my amps (1 x CA-5200 and 2 x CA-M400). I heard no difference. :-( The pre/pro still was audibly improved but the power amps didn't do much.
I also swapped out all my fuses (all with the HiFi Tuning Supremes) on the Pathos Classic One Mk III integrated (5 or 7 fuses...can't recall). Again, not much difference. Should have just stuck with the pre/pro and saved.