i burned mine in with use. things i noticed are as such:
amped, improved bass accuracy and tonal seperation over about a 120 hour period,
even after 120 hours, there was nearly no bass with portable devices.
after an estimated 500 hours, my proline 750's sounded perfect on any portable (given the fact all portables ive used are decent quality) but were lacking in volume, bass was there, maybe a little weak on the snares and kicks, but definately workign well on low power.
thousand hours+, i get a very sharp listenable volume, application of the zunes "jazz" EQ, sounds, so, good. i beleive in burn in....
FS: LDM+ xDDD jkjk. actually.. maybe, im getting IEM's for work, and my e-mu1616m powers my prolines very well.