I agree with @ghdprentice that live music should be your benchmark. Acoustic instruments and voices are the touchstone. I don't really compare components to each other but rather listen for how "real" it sounds in my system. A lot of gear can sound impressive but over time seem artificial in some way.
When I make changes I use music with singers I've heard live. I have an enduring sense of how their voice expressed emotion and I listen for that.
I do experience getting "used to" a certain sound and liking it, but that's because it corresponds to my expectations for sounding real. If it doesn't sound that way, I don't get used to it, I get annoyed by it.