Originally Posted by waynes world
Having said that, your test music is quite different from the music that I listen to (rock, progressive rock and electronic), so I wouldn't mind also hearing other people's impressions.
I haven't heard the M500s (or any of the other headphones you own), so you won't really have a point of reference, but these are my impressions:
General: These NEED an amp to shine, and it should be a relatively good one. They didn't synergize particularly well with my EF-2A, but were pretty nice with the Matrix Mini-i. Playing directly out of my tablet, laptop, or Cowon S9, they lost a lot of bass quantity and definition. They also need good source material - 320kbps mp3 or lossless - that's well-recorded to start with. They are uncomfortable. No getting around that. The clamping force is very strong, though that can be alleviated somewhat by stretching the headband. I have a pretty small head, and I was in pain after about an hour or two of listening even after stretching the headband.
Rock: Rock and metal are probably this headphone's greatest weakness. The treble is pretty bright (keep in mind, my main headphones are the D2ks, so I may be skewed here), and guitars can sound screechy. Cymbals can overwhelm the song. Recording quality is a big issue here - many rock artists don't have the greatest recordings.
Prog Rock: Can sound good, depending on what you're listening to (see the last couple pages for my impressions of Rush). Same issues as above (treble, recording quality) apply. Vocals are nice though. Pink Floyd sounded great.
Electronic: I don't have too much electronic, but it sounds pretty good one these. Bass isn't huge, but it has nice impact. Vocal trance sounds pretty good. Electronic music is generally recorded pretty well, which helps immensely.
If you've got good source material, a good amp, a liking for treble, and some pain tolerance, these will be perfect. While I initially trashed them, after listening to them out of a quality DAC/amp, I can see why they've gained the following that they have. When the planets align just right, these can be phenomenal. It's just that in my case, they don't align very often. I was looking for a headphone that could be driven by a mobile device and I have lots of poorly-recorded music (that I enjoy for other reasons), so these don't work for me.