Looks like i'm a bit late to the game, but this one seems interesting
A good friend of mine will be in Japan for a several days and interested in these. Are there anyone heard it before?
Yes the TH900 is definitely better especially in bass and lower midrange but TH600 sounds more linear ( some preferred this ). Changing the cups to woods will alter the sound but i don't know will it be like TH900 or not, never tried them