that's because they did sound better. When I got my 325s they sounded terrible I let them burn in for 4 days straight. AS PER INSTRUCTIONS. Sounded like a difference set of phones. and as I said I didn't listen to them and get used to them, I let them sit on a CD loop. They Played Much Louder and smoother...the people on here that doubt this, just never heard it.
Well here's my anecdote:
I bought the same headphones you did, and they sounded great out of the box. After 4 days of burn in with the same CD you used, they sounded much worse. Compared to new, they lacked dynamics, musicality and bass depth and slam. The soundstage became constricted, and they were so muddy that if I put them down on a newspaper for an hour, they left a stain and words became illegible.