What makes the biggest difference in sound quality?

speakers and cartridge tend to make the most difference IME, but you reach a certain level where everything matters.  

I'm finding that the "level where everything matters" is as much a curse as a blessing. The Absolute Sound is like the Absolute Truth, doesn't exist, couldn't be found if it did, so the fun lies in the process of endless tweaking.

Drivers> Crossover>DAC>Source>Amplifiers>Cables>Room Treatment>Fuses/outlets.  

EVERYTHING matters. All of it, every part of the audio chain is critical.

Your thread isn’t working out quite as hoped aye Ted 😉

Interconnects, speaker cables, power cords, or fuses?

None of the above.