I had the headset twice and he sounded each other. The first time I was fascinated by him, great resolution, though not for Bass fetishists but for 80 Euro top P / L. One could also quite good use of MP3 players it. The second time he sounded just too dull. In a very ausfürlichen review at the large headphone side and Community Head-Fi, the reviewer is a fact that it sometimes is in this model large series dispersion and that you can be unlucky and a bad model caught (easy Head-fi and Koss 100 DJ googling).
Anything else about burn-in (ie a matter that the headphones need some time to record himself) in any headphones I've experienced so extreme as in my first Koss 100dj. Out of the box it sounded really bad, after about 20 hours before the sound was great. So let definately the KH some time. (My second Koss 100 Dj contrast, sounds like months still bad).
Amazon also offers a headphone 30- day return policy, so you have plenty of time listening trial.