You'll find a lot of discussion in earlier threads here about break-in of equipment -
here and
here and
here and
here and
here are some of my favorite debates on it - informative and enlightening.
I relate the "break-in" phenomenon of solid state devices (which professional cred in the forum seems to dismiss) to experiences as simple as seeing a movie you like many times. The first time you see it, especially in a theater, everything about it is new to you, so your mind has a hard time encompassing it all at once. However, since it so inundated you with stimuli, you come away thinking that you absorbed a lot. The next time you see the movie, you'll know a lot of things that you didn't know the first time, and you tend to notice things in the movie that you didn't notice before since you don't need to focus on them. If you just love the movie and see it many more times, you'll pretty much be at the point where you can now process all of the stimuli in it that your mind is capable of perceiving, and you see it as a much fuller experience than you did the first time. However, the first time you saw that movie, it wasn't any different - the only change was the perception of the observer...you.
Just a theory, of course.