Normally, I would like the D2000 for Ambient for their spacious characteristic. I also enjoy Ambient from my Ultrasone HFI-780. Two completely different sounds, but I think it comes down to what kind of sound you like from a headphone. Though, I think PRO 900 may also be a consideration if you have not tried them. Those guys have some of the closeness of the HFI line, but really have a very surrounding soundstage. Also their resolution can give off an "airy" sound, though not at all like Denon D2000.
Just my take from what I've experienced with Ambient. I think Ambient can be a tough one. There are times I can't be without my HFI-780 for Ambient, and other times I would like a bit more of something. I guess it is really mood dependent. I think some Beyerdynamics may be worth a shot. I think the DT770 aren't quite adequate, and the DT990 would definitely do a better job. I have a feeling some DT880 may be enjoyable for Ambient. They are quite an elusive can for me right now, but sooner or later I will have them!