I love this headphone! Even owning the HD-800 I just can't part with it. What I got with the HD-800 was about 10% more of everything that the 600 does extremely well. I have also owned, and sold, the HD-650 which, “for me,” was a bloated and exaggerated sonic mess.
To get the very best from the HD-600, I strongly feel that one needs to pair it with a superb (not costly!) amplifier, have good-to-excellent source equipment and software, and replace the original cable for the one on the HD-650 (about $25-$33 on EBay). Currently I have it paired with a Darkvoice 3322 (currently waiting for the La Figaro 339) and it’s pure magic. The level of realistic instrumental timbres and detail, natural bass, and realistic ambience are spectacular. If I had purchased the HD-600 before the HD-800, I don't think I would have bought the latter (well, maybe I would have auditioned it, of course.
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I am at a loss to explain mention in some quarters of “lack of bass” and/or “rolled-off treble” in the HD-600. I have tried everything from Widor Organ Symphonies (the “Finale” of the 5th, for example) to Bela Fleck’s “Flight Of The Cosmic Hippo” (no better recorded bass out there) and the bass is full and deep without the unnatural boominess I heard from the HD-650. String timbre, high brass, and cymbals in well-recorded symphonic classical music is not exaggerated or grating (please note: “well-recorded”).
I listen to classical, jazz, popular and the great bands from the Mesozoic (Pink Floyd, Boston, Kansas, Alan Parsons, Genesis, etc.). Of less importance, I am also a classical musician.