That is the arugment I've been trying to put forth from the beginning, that it is really a case of the listener getting used to the sound of a new piece of equipmet over time and as a result it sounds better to them, thus "breaking-in" of the ears rather than the equipment.

I run into this all the time in tuning systems with EQ, and it's a bias that I have to fight. Over time, even a "wrong" tuning starts to sound "correct" to my ear as I get used to the sound. If not realized and fought, objectivity is compromised. The same is true of mixes of music I've performed - any mixing job starts to sound "right" after a while, no matter how it originally sounded.

New pieces of gear that have run through my studio (new equipment I bought for my film work or equipment designed by one of my best friends, who is a designer of audio equipment for some high end brands) at first listening sometimes sounds startlingly "different", and over the hours/days, they start to sound like the "norm" rather than "different".

In these instances, I have cross-checked the differences in sound both initialy and over time by using two examples of the particular piece of equipment. I use one only of them (usually because I only need one of them) and do not power up the other piece at all (in some instances, I've known that both examples are completely new since I've assembled them). After my ears have adapted to the first piece of equipment (what some people would believe as "break-in") I have performed an A/B blind comparison of the original piece of equipment to the absolutely new piece of equipment.

The result has always been the same - the used piece of equipment and the never-powered-on piece of equipment sound identical.