What makes the biggest difference in sound quality?

For me, the updates that have had the biggest impacts to my preamp and amps were power cable for the preamp and speaker cable for the amps. The power cables  for my amps also made a difference, but not at the same level as the speaker cables. I recently added spring isolation to my amps and that added more depth. I think it helps since I use tube amps.  

I've found speakers > amps > source > isolation >  cables.. Within all this the poorest performing link will place limitations on the best. For example, a great interconnect will get murdered going through poor speaker cables. Trying to make sure it all matters is important, or at least keeping that in mind as you go as your building a system. Ted, can you explain some of this from your own experience?  

Interconnects- significant positive changes.

Speaker cables- less significant positive changes.

Fuses- no changes. 

Power cables- less significant negative changes.  

@bjesien 

Looms are key. Because speakers are sold in pairs, you don’t tend to find people using two different speakers. But you find people using electronics from multiple manufacturers, and cable stew. Ultimately you would want an amp and preamp from the same manufacturer, and definitely a full loom of Interconnects speaker cables digital cables power cords from the same manufacturer and loom. Back in the day when I would accompany my dealers to some of their biggest customers, to help set everything up, I was absolutely amazed by the poor performance from six-figure systems with a hodgepodge of cables purchased here and there on AudiogoN. Nothing destroys performance more, and anyone who tells you differently, does not know what they’re talking about. What I didn’t ask with this question was acoustics, which is number one.

Everything

Can't really get a more ignorant answer to the OP's question.

It's as if the word "or" is mystifying to someone using the language for decades.