I actually already got a pair of Sennheiser HD-25 II, and they're very aggressive with super heavy bass and sharp treble. Since they're closed they're excellent for DJing and listening to that kind of music. Also got a pair of Grado SR 80 for easy home listening.
The one's I'm looking for now has to be more high end, refined, open and have a big soundstage with lots of detail, but without being too boring. Predominant use would be gaming, movies and some music listening, although I think that won't be very much.
Maybe the sennheisers are better for that after all as they seem more natural and have bigger soundstage with more accurate positioning and detail?
Also, I have no idea how the Beyers would pair with my NAD.
I would just use the HD-25 for your bass heavy music then, as that's pretty much what they're made for. Headphones which are good for gaming (open, big soundstage) don't usually do well with bass heavy music.
The Sennheisers have an excellent soundstage, but are a little mid-centric and boring IMO.
DT990s would probably be similar to an open HD-25. Bassy and "V" shaped.
You can also look at the Q701. More fun than the Sennheiser and very balanced.