Essentially the Denon is tuned for relaxed but clear listening with a strong low end and larger sense of space, the MDR-ex600 neutral and natural and finally the Amperior which has a flat studio sound, a little less-pleasant but engaging and with its own depth and richness. It's a sonic screwdriver.
What is surprising, especially in my comparison, is that as sharp as the Amperior can be, it's within these tones that aspects of the music are revealed. It's a lot of fun switching between the headphones and testing out how they respond, a bit like trying different scotches.
The more I do this, though, the more I start reaching for the Amperior. If I had to keep one it would be the Amperior, as it's the most versatile and accurate.
Glad to have the Amperior 'back' (never owned one but had the HD-25).
My new Amperiors with their ravaged HD-25 brethren in the foreground. Story of how this happened here:
Edited by Malfunkt - 5/27/14 at 8:10pm