I have a pair of these purchased from a Chinese vendor that arrived yesterday. I have a pair of KZ5 which have about a month of burn in. I prefer the sound of the KZ5 but that might change once I get more time on these brand new KZ6. Right out of the package the KZ6 is bright enough to make listening uncomfortable.
bsoplingerAgreed, out of the box these are too bright - to the point of fatigue. But, I can honestly say they smooth out quite a bit after burn-in. I've now burned mine in for approximately 36 hours using wide spectrum source material at a somewhat loud level. I wasn't a big believer in burn-in until now. The highs have definitely backed off a bit. The only thing that I don't like so much is the mids, lows and sub-bass have smoothed out too. That seemed to remove a bit of definition and cleanliness from those regions that were nice before the burn-in. I still think they sound excellent for the price. Just be patient and burn them in.