They don't sound similar, in any way. The TH-600s and 900s are much more clear and uncolored.
TH600's uncolored? I'm not sure what the definition of that is - could you explain what you mean?
I just got a pair of TH600's and though the box says reference headphones they are far from neutral. Lovely, Bassy and sound great. And my D7000's were their equal in every way.