I think a big thing the HE-500 has going for it is the bass and impact. Not necessarily just in the bass frequencies alone, but even in the mids, there's a sense of impact that adds body to the instruments. If you're not into bass, you should look into electrostatics. Those have great mids and treble. Especially treble. To me, I've not heard anything like it compared to my Koss. Because of the speed, you can hear a whole new level of detail in the trebles that I've not heard from any dynamic or orthodynamic headphones.
It all depends on your sound preferences. Do you prefer airy or syrupy? HE-500 I would definitely describe as fluid or syrupy, especially through my setup. The Koss is definitely considered airy. I do wish the Koss had the level of transparency my HE-500 has though. I've read that's due to the mediocre amp that it comes with, not the headphone itself. It'll be a while before I upgrade the electrostatic amp though. Those are expensive!
I find these two headphones to complement each other quite well. But I've also thought about grados as well.
Koss are nice, but they're definitely out of my price range, lol.
Edited by Ambien - 12/12/13 at 3:11am