"When making changes or adding things to your system, what makes the bigger difference in sound quality on preamp‘s and power amps? Interconnects, speaker cables, power cords, or fuses?"
This possibly could have been phrased more clearly, but I think the OP meant that *of the options listed*, what makes the bigger difference.
"And while power cords may make the biggest first impression, it is usually the last cable you replace, something like a mis-matched ethernet cable, an interconnect or a power cord going to something you don’t think matters, it is almost always the last cable that is perceived as making the single biggest difference when that cable completes the loom."
I think that this is the answer. In a highly tweaked system, it's the last thing you do that seems most significant, because all the previous improvements allow the most recent to perform at its best. Whichever order you upgrade your cables and fuses, the last one done seems most impressive. Or at least that's been my experience.
