Well, TH500 is with me for few days now. I found it very much to my liking. Compared to Sens HD650, they sound brighter on the top - the HD650 "feels" rolled off in comparison. I found bass cleaner and better defined with Fostex but not dramatically. Midrange is very different between these two: Fostex sounds as having a bit elevated "presence region" around 4 Khz; I probably would prefer "warmer" mids of the HD650. Both have about the same volume from the same amps I've tried. Both are light and comfortable on my head, no preference here. With slight margin, I probably would prefer 500HP over HD650. Lastly, by the sounds of Fostex, I would not have guesses they are planar or anything different than a decent dynamic headphone. Overall, very good headphone in my view.