If it's mainly for rock have you considered either the Grado 225is or 325is? I haven't listened to them but I hear that Grado is exceptional for rock music. Other than that I actually own the HD 598's they would not be a bad option. They have a very large soundstage with great instrument separation and some nice sounding mids. They are a decent all rounder but I find the bass to be a bit lacking. Not in the sense that is is necessarily bass light, there is just an issue with distortion on bass heavy tracks. I have also found the HD 598's to have a very butter smooth/polite sound and I just can't really see them being a better fit for your grunge and alternative music than some of the other options. Despite this, I think the HD 598's do well with a good variety of music and even excel at acoustic and jazz music. All in all, they would certainly not be terrible but from the sounds of it Grados might be more up your alley I think.
The Grados are not good all-arrounders until you get to the RS series.
The 598 is a good choice, although I personally prefer the Q 701--in part because its greater clarity over the 598.
