Well, HD600s are said to be laid back as in they are not aggressive; everything sounds so natural with them. As for your genre concern, yes they are a very good all rounder, but I personally think that they sound great with Rock genre (Hard Rock, Classic Rock, Alternative Rock and J-rock are the Rocks I listen to). Yes, the presentation of HD600s is certainly different from the Grado in-your-face, they are more relaxed comparatively as in you can hear all instruments but not one will 'drown' the others. What I mean is the instrument will only stand out when the record actually highlights it. This is particularly good because my mind wouldn't be 'tired' of all the background electric guitar before the typical guitar solo during the bridge of a song. And this is why I always end up air-guitaring and pressing the repeat button! This is my personal preference and opinion though. However, if you ever get the HD600s, do give them some time, they are not cans which would make you go WOW when you first heard them, but you might come to appreciate how natural these cans sound after like 50 to 100 hours of listening. Hope that helps! Have fun in Head-Fi.
Yik
Yik