I feel I must further update my impressions of the AD2000X. I'm not sure if it's the headband adjustment, more burn in, or just getting used to the signature but this headphone is beginning to immensely impress me. This is simply the most impressive headphone I've owned in portraying a sense of rhythm and drive in music, and simply the best I've heard modern rock in my system.
If you like bands such as Five Finger Death Punch and Godsmack, this is your headphone. The level of articulation with quick guitar licks and tight, powerful, and punchy drums is just ridiculous. It's nothing close to neutral but quite addicting nonetheless. Mids are still very forward and upper mids a bit aggressive at times but it's balanced out nicely from when I first got them.
I've never heard the original AD2000 so I can't compare but I've seen similar descriptions before. Of course it's also good with other genres like EDM, some acoustic stuff, and I even enjoy them with a lot of hip hop due to the articulation and clearly defined vocals. Going by memory, I think I could put this in the same class as the Beyer T1, though to be fair I think the Beyer is overpriced new. I am also working on buying an HD800 in the next 2 weeks or so to compliment the AD2000X.
Bottom line, If you want to pick apart your music and analyze all it's properties, buy another headphone. These are designed to pull you into the music and take you for a wild ride
Of course all this is IMO, YMMV, etc.