I have the A900s, and seriously, these aren't made for Metal music (in my opinion). They don't suck at it, but to my ears they don't do Metal well; at least, not the way an average metalhead likes it.
The sonic signature of the A900s is such that it has relatively lesser mids than the average cans, and this turns most metalheads off since the palm-muted chugs will sound less powerful (the lowmids). I don't know, but it is either that they are recessed in midrange, or most other cans have a midrange boost.
The A900s are, however, great for detail, so if you would like to hear well recorded, mixed and mastered albums, these cans will do it. A good example of such an album will be Opeth - Damnation. In the album there are fewer of those chugging rhythm riffs and the entire mix is crystal clear, with lots of atmospheric keyboards background. These cans shine on it.
If you are, say, an In Flames fan, those riffs will somehow sound a little lacking in power, although the entire overall sound is still crystal clear.
These are of course, just my opinions. So, choose your headphones wisely.