Interesting!!! I’ve had a brief chance to hear the HD600’s but never owned a pair personally. I have one friend who swears by them, and then he went all the way to the “top” and bought HD800’s.
I have a taste for upper mids/treble at times, but I think the non-S 800 is overkill in a whole variety of ways. Just looking at a measurement graph for it makes my ears wince, hahaha.