Seems like the Grado SR60i would be a perfect choice for you. I listen to a fair amount of classic rock myself with these cans and I love it. The SR60i is an open headphone and while it sounds airy and speaker like, I don't think it has a very wide soundstage. However, it should be better than the PX200 IMHO. The SR60i was bright sounding out of the box, but after a fair degree of use and burn in, the highs have become less 'hot'. Midrange is the best part of these things I like. I find the bass response more than adequate even though it is open- I was a bit of a basshead earlier, but I felt right at home with the Grados even out of the box.
For better bass response, I think that the SR80i would be more apt and the Alessandro Grado MS1 sounds more balanced than the aggressive SR series. Do try them out as some folks do not like the aggressive sound signature of the SR60/80 or with the fit and comfort with them. Still, for rock and metal, I don't think one can go wrong with these.