I don’t think you need to burn in headphones but I do know that very loud playback DOES change the sound temporarily. My father has pretty severe hearing impairment on one side, enough that hearing aids just barely help, so he uses his headphones at extremely high volume on only one side to gain some degree of stereo because otherwise his world is mono. Any time he has tried my headphones, for a period of time afterwards there is a very noticable mismatch between the drivers. Don’t know what specifically is happening but its happened on 3 different sennheiser headphones and it goes away completely eventually. This is also at volumes I don’t recommend anyone who’s ears currently work expose themselves to so this is hardly proof that regular volumes do anything to the drivers… but I am quite sure that it is actually possible for playback to alter the drivers.