Hi Mapman. I have had similar experiences. Initially, changes may sound like an improvement, but sometimes, especially with gain in high frequency extension, the presentation is more forward and overly bright. Similarly, with greater emphasis in the bottom end, extended listening may expose a heavier, looser bass, which can also affect the mids. This is why I often have issue with a/b comparisons. Living with a new component for awhile, not ignoring break-in and synergy, is likely necessary for fair assessment.
Think twice before concluding some thing sounds better
Often anything good that is merely different seems better. So many aspects of sound, things to listen for. Takes time to really know what parts are better and what might actually be worse in a complementary sense