I have heard no decisive facts to ever convince me speaker break in is real.
However, prior to even getting an interest in upgrading my sound system, the 'first song sounds crappy' scenario bugged me enough to ask an audiologist about whom I know from my years of working at a hospital.
He had an actual scientific name for this effect. He also explained that for a hearing test to determine at what point your auditory senses are beginning to fail, it is just as accurate to start at the inaudible and move up to a point where the subject can indicate he hears something audible.... However, it is always done the other way around to allow the subjects ears to grow accustomed to hearing the sound as presented by the ear phones.
