I had purchased a Sony CDR-375 due to having seen a plug about its character...it definitely has a crystalline top end, smoothed midrange, and an overall strangely shifted character. I noted that it has a 4558 op amp in the output, which is old and slewy (which is great for certain things). Definitely not a "wide bandwidth/clean" opamp, for program purposes...
This machine must be oversampling. I've since acquired a few older Sony CD players, and note timbral differences, with the 1993 unit being pretty honest (but a bit gritty in the top).
Discussion in the DIYaudio.com fora pointed to oversampling as the culprit. Two to four-times oversampling seems to shift upwards the overall spectrum, due to increased timbral density. Even congas and female voices seem to have a slightly higher fundamental (or the energy is upwardly shifted due to new overtones??). I found that this messes with the balance of a drumset (real or electronic). Dead Can Dance's "The Fatal Impact" has a nice balance between synth conga and synth kick drum, a nice, stumbling dread. I did not enjoy how it changed on an oversampling machine. I tap my toes and move a little to this beat, I like it a lot; don't mess with it, don't change the original intent of the music.
I note that some things benefit (the guitar and overall "snap" of Diana Krall's wonderful "Live in Paris"), but other things do not, as might be concluded/expected. C-Tec's "Cut" will peel the skin and hair from your face and skull. You didn't need that anyway.
One DIYer posted that a friend brought over a CD of his drum playing. Upon hearing it on the other system, he stated bluntly (and truly), "That's not my drumset." The DIYer had a setup allowing for the selection of sample rates, and upon selecting 44.1/16, the player was satisfied. I will surmise that this is the rate and depth at which it was originally recorded, etc.
Some players have SPDIF and optical out, allowing the use of external DACs; some of them are specifically non-oversampling, yet are capable of it with additional hardware (the OPUS from twistedpairaudio.com), and sport the most modern converters with truly extreme specs. Because it's DIY, you can find out for yourself.