After reading this forum, I just had to get my hands on the CKM500. I haven't burned it in yet, but I am pretty disappointed with this ear phone. The high notes sound very harsh and artificial. It's like they forcibly increase the volume on the high notes. I really prefer my CKM55 over the CKM500, but I will give it a couple of weeks and see if they improve with burn in.
They sound better with some amount of burn in