Almarg - It isn't just your Stax headphones. A few years ago, I was forced for housing reasons to not listen to music for a year. My wife & I get to our new house and I set up my mid-fi Paradigm speakers - which haven't been played for a year -- and within an hour concluded that they sounded terrible and were done and needed to be replaced. After a few days of sporadic use, they regained their rich and pleasing - if undetailled - sound.
My conclusion is that break-in doesn't just apply to new equipment, but potentially to any gear that was left lying around for a while.
My conclusion is that break-in doesn't just apply to new equipment, but potentially to any gear that was left lying around for a while.