The equipment CAN’T change as much as we do unless something is seriously wrong with power grid
That's true only if you assume everything that is audible has been measured. Or that the tests have been done to prove or disprove this.
I don't assume the first, and have never read of the latter.
As an engineer who relies on measurements, I know I hear things which change over time which I have no explanation for. I once left my gear off over a weekend, came back, turned it on, and thought, man, this sucks. 48 hours later the sound came back. No idea why. I replaced caps in a pair of Focal speakers and for about 72 hours heard weird surround effects. Tones and instruments appearing behind my head. No changes to room acoustics from when I heard that to when it ended. The latter case tells me there may have been very subtle HRTF (head related transfer function) issues coming up. If so, no standard measure of capacitors would have easily found it.
As for the Luxman, I do have a cold right now, so bad time to judge. :)Â
Also, I kind of want to remind everyone, it's kind of a shame we don't see more invention of how to measure amps, caps and cables. Almost all the measurements I know of except Jitter predate the CD player. They were fine for their era, and not to be discounted, but we live in a world with computers, automated signal analyzers and cheap data capture. It is a real shame we haven't attempted to push the state of the art for discovery and measurement in audio.
Best,
E