All I can say is WOWSER, out the box they sound divine, can't wait for the burn in period to have passed. Through my Cowon Plenue P1 linked up to the Chord Mojo they're sublime so so sublime Happy Happy Happy Happy...
EscapismThey don't have a burn-in period that I know of. I have the non-PH version and it sounds exactly the same now as it did when I first got it (at least 100 hours of listening so far).