Denons handle rock nicely, but metal they certainly don't, as they have far too slow drivers for the genre. I would never recommend Denons for metal alone. On the other hand, the Ultrasones have very fast drivers, which makes metal much more enjoyable.
Also, EQing is very useful to even any peaks or dips on the frequency range. I found that by toning down the 9.5K band (one example) on the Pro 900, it solves a lot of the piercing highs that most people find them to have.