I bought a CD3300 a couple of weeks ago. I think it's well worth the $499, but I don't have much experience listening to players at this price point and above, so bear that in mind as you read my opinions. I play several instruments, and I've played in bands in reasonable acoustic environments, so I know what particular styles of rock bands "should" sound like; that's my benchmark.
I listen to the CD3300 mostly through Sony CD3000 headphones. The combination generates plenty of treble: cymbals, hi-hats, snares, chimes, triangles and other high pitched percussion are clear, and I've been startled by the new crystalline quality of some sounds I've heard in familiar recordings. On one of the tracks on Steve Cole's "Stay Awhile", I heard a choral keyboard part I've never noticed before. On Nelson Rangell's albums the percussive "sweetening" has good stereo placement, and the sound is exciting.
There's plenty of attack in drum sounds, the impact of bass drum beater on skin is clear, and snare drums are sharp. Steel string acoustic guitars have a lovely sparkle, but the CD3000s may be largely responsible for that, they're known for their good reproduction of metallic sounds.
On Joni Mitchell's Travelogue, Larry Klein's bass is rich and articulate. Electronica bass is also detailed, with plenty of thump and sizzle on Layo and Bushwacka's "Night Works". On David Sanborn's "TimeAgain", Christian McBride's bass is woody and resonant, and David's alto sax has a reedy "phloom". On this recording I'm now hearing some slightly distracting sax key noise I haven't heard before, I guess this means the player is revealing.
I've never listened to a dedicated headphone amp so I don't know how good the CD3300's amp is, but it seems to generate quite a few milliwatts; the volume knob doesn't have a scale, but on an assumed scale of 1 to 10, I can't handle anything louder than 2 (although this thing, like the guitar amp in Spinal Tap, goes to 11 in my opinion). I've also listened to the player with Etymotic ER4Ps, and in my experience they are ruthless at uncovering noise in the signal path; I don't hear any here. On the other hand, I've read that a good headphone amp should improve the ER4P's weak bass, but this headphone out doesn't seem to do that, so maybe that's a mark against it.
I like the CD3300 a lot, but I may not be qualified to recommend it to you, I haven't heard any of the other players you're looking at, and all my headphones are much easier to drive than the HD600s.
What CDs are you listening to currently? Perhaps we have an album in common and I can tell you what I hear from the CD3300. If you have any modern saxophone jazz, I'm likely to have it too, and I have all of Pat Metheny's albums.
