I don't think 40 second intervals are even close to long enough to acclimate your ears to what you are hearing, and allow you to appreciate the differences that matter. Your strategy was extremely artificial, and your head cannot have been into the music at all -- just the sound. Your brain will also under such circumstances attempt to normalize what it receives.
I had friends over the other night, and we listened to a bunch of music -- several songs from a given LP or CD at a time -- in a casual, talk-over-it-if-you-like-kind-of-way. People seemed a helluva lot more inclined to talk over the CDs than the LP. They even talked about how good the CDs sounded. But they shut up (more anyway) and listened to the music when the LPs played. Not a scientific test, by any means (but then neither was yours). But I find this typical.
I had friends over the other night, and we listened to a bunch of music -- several songs from a given LP or CD at a time -- in a casual, talk-over-it-if-you-like-kind-of-way. People seemed a helluva lot more inclined to talk over the CDs than the LP. They even talked about how good the CDs sounded. But they shut up (more anyway) and listened to the music when the LPs played. Not a scientific test, by any means (but then neither was yours). But I find this typical.