Regarding the treble, I guess I could "6moons" it up and write something like "roll off" "effortlessness without subliminal fatigue and greater treble transparency didn’t involve any superficial and stressed analysis" - doesn't change the fact that the He500 treble is rolled off, contributing to its sweet sweet sound (that's not a bad thing!).
I disagree that the treble is rolled off. At least to my ears it doesn't sound like it's rolled off. Sure it hasn't got the amount of treble of a DT880, in fact it has way, way less but I wouldn't called it roll off. It has just the right amount to bring sparkle into the music. I would call the LCD-2 treble rolled off that's for sure.
I can't comment on the HD600/650 though. I haven't heard them through a very good amplifier yet.
But still, the HE-500 is just effin sweet (properly amped of course).
Oh and also: HE-500 Slow? I don't think so... (Ok, if compared to Staxes, yes it is slow... a lot slower).