[MegaMushroom]

After searching around for sometime I've come to the decision that I do in fact need new headphones quite badly.  The unfortunate thing is that I'm rather poor at the moment meaning that I won't be able to afford an amp.  I've been looking to upgrade from my Koss UR-40 for sometime now and was wondering if I could get some help with selection.  I've been looking at the Ultrasone Pro2500s.  They do fall within my price range of around 230ish dollars.  My question is: are they any good for listening to rock/metal?  Think Pink Floyd, Led Zeppelin, Mastadon, Deep Purple as well as some more techno music like Daft Punk and RJD2.  I've heard some rather mixed reviews about the Ultrasones, and was wondering if there are any other headphones out there that match or are better for the price.  And I am searching for open back.
 
I'm also looking at the Grado Sr325is...
 
EDIT:  Is there a difference between the HFI-2400 vs. the PRO-2500/2900?