Dubstep and metal have pretty much polar opposite needs when it comes to headphones. Dubstep likes the U shaped strong highs and lows headphones, while metal likes the strong mids headphones. So I'd look at something that was more balanced with some added bass hump (which is usually popular).
In my experience, Denons are better all-rounders than Ultrasone (this is comparing the Pro 750 to the D7000). Ultrasone will give you much more subbass (if you're big into that, definitely the most popular type of bass), but won't be that great for metal (mids are quite recessed). Denons will give you more subbass (which is lower than subbass, and a bit less common in music because of how popular midbass is), and will be plenty good for metal as well. Modded Fostex T50rp's tuned towards mids make some great metal-only headphones. My Rastapants II-M's are fantastic with metal, but very specialized. For another well known mids headphone, you may want to take a look at Grado. I don't have one, but you might as well keep it in mind if you ever want a metal-specific headphone in the future, I've heard good things. :)