I tried the D2000 for a few weeks, and while I enjoyed it, I don't think it is on the same level as the Pro 900. The Ultrasones go deeper, hit much harder, and sound quite a bit more refined. I found the Pro 900s for 350, so for the extra hundred dollars or so, they are definitely worth it. Now if they were up around 500 or 600 dollars, the upgrade might not be worth the cost. I did love the supreme comfort of the Denons though, and if the D7000 are a bit better than the Pro 900 (which some who have heard both declare), then I wouldn't hesitate to upgrade once I have the money.
I highly recommend you try them out someday if you can, because if you enjoy the bass on the D2000, I'm sure you'll dig the thunderous bass of the Pro 900. If you can't find them for the same price I did, however, you might not consider it worth 2x the price of the D2000