I should have mine Monday. I do have a pair of HD515 and I've heard the HD600 and HD650. The Sennheiser sound is very natural, on the warm side, but detailed. Voices rock big time, the midrange is their signature, do not expect really low bass, but more of a tighter one. Highs are pretty smooth. Lots of good resolution, excellent soundstage wide and deep. I can wear them for hours on end with no problem.