Not an expert, but parroting the people who act like they know what they’re talking about.
Quality cannot be quantified because there are different measurements. I’d say any one measurement can be quantified, but how they are weighted into what sounds “better” is subjective. Some (misinformed) people say bitrate is king, and already in this thread you see dynamic range as another important factor that has nothing to do with bitrate.
Other things that affect perceived quality can be noise/scratches (vinyl sources) and the master itself. Different remasters of the same album can sound different because of decisions the remastering employee(s) made.
You may have a somewhat hard time finding scientific research or commercial interest in the topic, because it’s already “solved”. 99+% of people are totally happy with 320kbps MP3, and even CD-quality FLAC is cheap enough to store. Services like Spotify default to a “normal” quality around 96 kbps. There might be viable researched published around 1980-2010 or so, when storage and bandwidth was more expensive.
What is still costly is video delivery, so I’d turn to papers published by Netflix and others to see the state of the art in subjective quality evaluation. Ex. here. And hope that audio is mentioned somewhere.
The best sources for more info, that I know of, are HydrogenAudio and Steve Hoffman music forums. Audiophile communities are plagued by pseudoscience that these two places seem pretty good at avoiding. Maybe you can ask there.
Also, I wonder if it may be less effort to just secure new copies of the files in question.