What makes the biggest difference in sound quality?

Good one.

Yes, Yes my little flower, yes, yes. You want a what? DIVORCE! I'll one up ya, NOW!!! I divorce thee, I divorce thee, I divorce thee.
I'm takin' the Eastern way out. Makes since to me (I think that's the right since, sense, cents)?

Regards

Room and Speakers obviously, however the Pre-Amp is the heart of your system which can really make or break it.

I have heard this from almost all hi-fi equipment dealers that speakers make the most of the difference, spend 75% on speakers etc.. Only one from Overture, DE said it is 50% speakers and 50% equipment that I agree.

75% Sound like a good number for a high end system.

However the leading question was aimed at preamps and amps (fuses, power cords, cables, etc.)

Most of the answers confirm with the premise of, “We hear what we want to hear.”

… what makes the bigger difference in sound quality on preamp‘s and power amps? Interconnects, speaker cables, power cords, or fuses?

What makes the biggest difference in sound quality is room treatment, followed by speakers and listening seat setup, followed by the gear itself.