What makes the biggest difference in sound quality?

As I learned today, I’ve been greatly underestimating the power of room treatments. I Installed a floor to ceiling bass trap in the most offending corner of my room and I’m astonished. Spent the rest of the afternoon recalibrating my sub to the “new room”. Best bang for the buck upgrade yet! 

As everyone has pretty stated everything matters and is important, but that is where i differ with most…

Let me go on the record as the outlier from the group with “everyone”.
Specifically with respect to the question of:
 

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? 

I believe none of the crap matters much, and certainly not the power cords and fuses.

But I may be a robot, and I believe that I am passing the Turing test.

I believe none of the crap matters much, and certainly not the power cords and fuses.

Hearing aids work,  you should try one 🙏. 

The four items you mentioned, interconnects, speaker cables, power cords, fuses, all are passive components. They can’t add anything to the audio signal, they can only act as a filter and take part of the signal away.

Fuses and power cords are not in the signal path. Assuming they are well dimensioned to allow for the current peaks your amplifier asks, they can only help reduce electrical interference.

Interconnects and speaker cables are in the signal path, they can directly influence audio frequencies. On top of that, speaker cables need to have low resistance in order to deliver the current peaks your speakers require, assuming your amp is capable of delivering those.

I’d say of the four items you mentioned speaker cables can influence sound the most.

None of these four components need to be excessively high priced, just choose them carefully.

Every Gear including the Room, I think the room is very important if this is not done right no matter type of gear you use it will never reach its full potential.

Audiophile tends to fill the space with diffusors but i think a 60-40 Ratio works well.

60 percent absorbers and 40 percent difusors