"Possible sources could start with the quality of input materials (e.g. CDs or LPs)"
I used to think this was more of a factor in the past than I do these days. I really think system related issues are a much bigger factor, though I know a lot of people find modern "louder" recordings to be a source of fatigue. That is a likely category of recordings to cause listening fatigue, but I find many modern "louder" recordings to actually be quite good, only a small % blatantly fatiguing. I wonder if some are actually designed to grate on your nerves rather than happen to come out that way.
I used to think this was more of a factor in the past than I do these days. I really think system related issues are a much bigger factor, though I know a lot of people find modern "louder" recordings to be a source of fatigue. That is a likely category of recordings to cause listening fatigue, but I find many modern "louder" recordings to actually be quite good, only a small % blatantly fatiguing. I wonder if some are actually designed to grate on your nerves rather than happen to come out that way.