Exactly. The muffled highs on the HD600 really get me annoyed. Like when I hear some singing, and they start hitting the high notes, instead of hearing those high notes, the singer's voice fades out. I'm also annoyed at how 'balanced' it keeps everything. Like the singer is singing his soul out and should have dominance on the song, but the HD600 keeps him having the same weight as the background singer. Sometimes the background singer is louder! Or, if the lead guitarist is wailing away, it doesn't take prominance in the song like it should. It has about as much weight as everything else. I feel like I am not hearing the song as it was originally recorded, but in the more gentle format the headphones are presenting it to me in. "Everyman is treated equal even if they aren't equal."
The HD600 gets the tone right, but the rolled off highs, the somewhat distant sound and restrained balance is just aggravating to me. They sound good, but it's like they aren't being fed enough power. They do good for music when I'm trying to study or go to sleep because nothing just explodes in my ear, but I also feel that gentle presentation robs some music of a lot of its emotional impact. I keep sitting there 'wanting a little more.' I'm keeping them around, especially to hear them out of a Zana Deux when I eventually get one... but I can admit the flaws of the headphone coming out of my headphone. At $300, they seem like a bargain for a 'world class phone,' but they are much more expensive than they look when you have to put so much expensive EQ behind them to get them to sound like they should. I guess I'm not a big fan of 'polite and overly balanced' presentation. I need something that grooves. I'm getting the SR80, but I'm not a fan of bright phones that stab my eardrums, so I'll see how accustomed I can get to the Grado sound.
My perfect headphones would be the HD600s unrestrained. Let the main singer go. Let the guitar player wail away. Don't roll it off. If he dominates the song, let him dominate... and let the music come forward a bit.