I decided to check these headphones out again to measure them. Here's some frequency response measurements:Blue - TAD500, Red - HD600Measured on a MiniDSP EARS with HPN compensation. A note on MiniDSP EARS measurements: Artifacts typically occur around 3-5 kHz in which the EARS show crazy dips and/or peaks which isn't actually there in listening. Treble also isn't too entirely accurate relative to better and more expensive measuring equipment. For example, I don't think the treble response is recessed in comparison to the HD600.I remember really liking them and I'm glad it's for good reasonThey sound very neutral is what I mean.I did a detachable 3.5mm cable mod on these. I re-terminated the stock cable so that it can be used with the detachable cable mod which will also be included.I think these sound more balanced than the AD2000 and AD2000X. I might like them more than those too. I think they're at least as good as the HD6X0 series. The fit is much better since it's not using a 3D wing system used on other ATH headphones. The earcups also articulate unlike the other ATH headphones. These were released only in Japan so these never really made waves here in the US or really in the west. The earpads are very soft and comfortable so even if my ears touch it, it's still comfortable to wear. The headband uses a pulley system unlike the elastics system in AKG headphones and so is a much more reliable system that should last essentially forever. The headband has lots of cushion and uses a type of fabric on the underside. I guess the catch is that it's kinda creaky at the joints so some WD-40 or some sort of lubricant can be used if it bothers you too much.Some minor imperfections on top of the headbands and on the lips on the earpads. Nothing major.From a smoke-less and pet-less home.Let me know if you have any questions!