I know an amp manufacturer in Colorado who doesn’t believe electronics improve with break in time, but they do. I couldn’t tell you why for the life of me, but I hear it. Klaus may have thoughts on this.
Power cables, interconnects, you can hear those changes too. I haven’t done much research on fuses, but even in my ignorance it wouldn’t shock me to hear a difference there too. System resolution plays into this - LO-FI gear won’t be as obvious, maybe nothing audible at all. People in the hobby running Odyssey gear are not LO-FI...
Sad to say, I was drug kicking and screaming to the concept that you can hear everything. Improved feet on your gear, spikes, speaker stands, racks, and damnit, dedicated AC lines, improved recepticles, the list never ends. The changes you hear may not be worth the cost, and some changes make it worse, but you can always hear it. Ugh.