What makes the biggest difference in sound quality?

@holmz :

We hear what we want to hear

Then what's the whole point of the whole discussion on Audio? Including the "room" discussion?

^That is true^.
But the OP asked the question specially about the 4 items he/she mentioned.

They did not ask about “the room”, however it is an area which is more likely to get value happening, than a fuse or power cord IMO. Just that it was not the OP’s question. IMO It was worth mentioning, but again it was not the primary question. Certainly I would abide spending money there before putting in a cable. One can usually sneak in a cable, with hope, than trying to convince a SO that some anti-WAF room treatment is a good idea.

Like @rudyb said a few posts up, I mentioned early on that speaker cables should be short and low impedance.

And.I offered my opinion after the “everyone” post. And the OP can ignore it.

Many of the other posts offer “Synergy” and “The ensemble” of gear, and also delve into the room, speakers, etc… which was not part of the OP’s question.

FWIW, I generally suggest one pours all their funds into speakers first.

If there was some evidence from manufactures showing that power cords, for instance, lowered noise into the system, then it would be a lot easier to abide them over just flowery words. I can see how they could work, but I have no idea if there is RF coupling into my system, nor do I hear cell phone sounds coming through the system like we used to hear in cars (etc.). It might happen I dunno. A ferrite core asking as a choke seems like a good idea, but I have to assume that the manufacturers designing the power supplies know their stuff… and that the massive capacitor banks obviate the need for special fuses.

Most interconnect wire is spaced for impedance and capacitance, but many of the assembled cables are sold without specifications. It would be easy to alter the sound with high capacitance or inductance, however I cannot easily ascertain from the looks alone how they might sound.

That’s a very long cumbersome way to express your belief that cables have zero impact to the performance of any audio system. And since you are also of the belief that “we hear what we want to hear”, I take it you never tried (as in listen) for yourself? 

I still have to pick my jaw up off the floor after installing Duelund Bypass capacitors to my crossover

@yuviarora - yep! me too