Hey KayoDot,
I would go with the AH-D2000. Very comfortable and because of their sound signature, they never seem to get boring. I could listen to one song for hours on end and it'll be brand new again just because the A2000 gives you this amazing listening experience. I wouldn't think twice on this beautifully designed and insanely sounding closed can. It's truly one of a kind. If you really wanted headphones with less bass and flatter sound, just go with an open back, ie: AKG702, HD595, DT990, and you know the rest.
Honestly, the A2000 is one of the best closed cans I've ever listened to and I can't wait to upgrade to it's bigger bros the A5000 and A7000 within a few years.
The A2000 couldn't get any better. If I was to describe a perfect closed can, without a doubt in mind I would firstly mention the A2000.
GL on you decision, but once again, all I can tell you is not to over look this can or think twice about it. You can't compare a DT990 to it really. Like you, I've had a hard time deciding for a long time about what to get. But now, I'm extremely glad I went with the A2000.
Yeah, I could have had a good time with the HD650, AKG K702, or DT990s which I wanted before, but I knew after using them for a few days that they'll get really boring after a while and before I knew it, I would have purchased the A2000 anyway. Heck, I even purchased the above and used them for a week before they got all flat and boring on me; I felt I needed something with a spark. But, I didn't want to waste more money and just purchase headphones that compliment, so I just went straight with the A2000 and I don't regret it for a slight second or think about going back to the HD650, AKG K702 or DT 990. I'm 100% completely satisfied with the A2000.
Let me tell you something man, I put these babies on everyday and I know I'm going to have a good time...I know I'm going to feel like pumping up the volume and just have a great time. I swear not a day passes by where I feel bored of the AH-D2000. They always make my day, even if I'm having a long day.
It just couldn't get any better, thanks Denon!