@lcherepkai, I don't like what you are doing. Love it. When listening to different fuses I briefly inserted a Cu. tube I cut to the correct size as a reference and thought I would find the fuse that sounded closest to it. I tried a bunch including Synergistic Research Blue, the most expensive, that I rated about middle of the group. I decided to leave the Cu. slug in place. I could not go back to a fuse after this.
The amp I used for experimentation is a DIY Neurochrome so I have no problem modding it. After some time I decided to direct wire the input bypassing the cheap plated fuse holder by soldering in some 14AWG OCC Ag. This was an improvement again but now does not allow for swapping out different metals as you are so keen to hear your findings on Tungsten, Rhodium and also Cobalt should you ever get a chance to try.