Please don't start a flame war. Like it or not, in my OBJECTIVE experiments and I made a lot, nearly everything make a difference beeing wall duplex, cables, vibration control, room treatment and FUSES!
I've been where you are, so let's start small, with terminology. Your tests are what's referred to as subjective. Objective would involve provable, repeatable, factual numbers from laboratory instruments. Subjective means you are deciding what's better by listening and it is called an opinion because it can't be proven as fact. Another person might not agree with your assessment of what's better or they might.
Subjectivity definitely has a place because without it we would not know which problems are the most unpleasant and should be minimized when a tradeoff is necessary during the design phase. This fuse I imagine does not have any signal going through it and studying how we hear (and see) will clarify why you can hear absolutely everything you change in and around the house reflected in the sound of your system.
The short explanation is that we hear primarily with our brain, not with our ears. (Same with vision, just for the record.) Very interesting stuff, I promise you. It was well known by scientists more than 40 years ago when I studied it. Check it out.