Well, you’ll be happy to know that I think the XPA Gen 3 does not use any fuses. It looks like it uses a circuit breaker instead. I would advise you to wait until you got a new preamp before trying fuses (don’t spend any effort on the XSP). I have tested several different fuses and think that the Isoclean fuse is actually the best all around. It’s actually the cheapest, and you can get it for $32 on ebay direct from China (I’ve purchased many Isoclean from the ebay seller hongkong_basket). I have not tried the very expensive Audio Magic fuses.
I’ve been participating in another thread and this guy went from the XSP-1 to a Parasound JC2 (way above your budget), and had significant improvements:
https://forum.audiogon.com/discussions/help-choose-best-amp-preamp-combo