I have the HD598s but personally didnt like them with metal. Although they are fantastic headphones otherwise (I used them a lot for movies, tv shows, gaming, soundtrack) but I lent them to a friend for a few months now.
I was very happy with the Grados 325i, so much so that I wanted to get the RS1is but I was unable to demo them. I ended up with the HE500s after demoing the HE6s. So far no complaints with metal, really enjoying them.
What didn't you like about the HD598's for metal, lack of bass? Just curious.