I own both the 598 and 600 and as long as recordings are good to great, the 600 is pretty much flat out superior and there is nothing about the 598 that I'd prefer over the 600.
However... Yep, things are never that easy. Most recordings that I'm faced with do not fall in the 'good to great' region and as a result I often find myself agitated because of how the 600's render music. Especially lack of detail in the middle of the sound stage, but also the lack of detail in cymbals, anemic bass, etc. If I can listen to a one hour deephouse mix and be perfectly fine with how everything sounds, it's pretty much a best case scenario for me. The 598 however, is a step below the 600 in resolution and as a result, once I get used to the 598, I don't notice bad recordings nearly as much. Yet the 598 is still agreeably close in terms of imaging, soundstage and balance.
Both headphones at their best though, the 600 sounds significantly better than the 598. The decay, bass and natural sound on the 600 are dropdead gorgeous and the 598 doesn't have anything like that.
Edited by SunshineReggae - 4/22/13 at 9:21am