I agree, the source file is all important. Different remasters no doubt sound different. In my car example, I’ve repeated the test several times. When I play the track from my phone’s memory, it sounds better than streaming even with the example same version of the song. The most noticeable part is the bass. From the phone, the bass is much more like a quick “punch,” and when streaming it’s more of a quick “shove,” if that makes sense. “Tighter, faster bass” might be a metaphor I could use.
Last night I copied one of my favorite CDs to a black CD-R and the difference in sound quality between the 2 discs was quite apparent. The treble was much more laid back and “tamed.” I could hear micro-details better. It’s too early to conclude which version is better as they both have their pros and cons. I’m interested in the “why.” Does one disc have more read errors than the other? If not, then I conclude that the way the data (the exact same data, that is) is arranged on the disc matters. The precision of the pit spacing, the width and depth of the pits, and the material of construction of the CDs may play a role. If it’s all the same data and the read errors are minimal, then what is happening before the buffer is having effect on the sound.