I've had the DX1000 for a year; the D5000, for about 15 months. I'd repeat now everything I wrote about these phones several months ago in numerous posts.
In a nutshell, I can agree with much that's been said in this thread on both sides. The Denon's are absolutely neutral, a perfectly safe buy for those seeking top-to-bottom neutrality. (Now, as we know, many people are simply unfamiliar with a strong 30 Hz and may not enjoy the experience, but that's a matter of taste.) The Denon's are neutral full-range phones; total keepers. Period.
The DX1000 does something to everything played on it. It adds a little bit of echo and a not insignificant measure of warmth. But, surprisingly, this is so well-done that the result is not an echoy caricature of the material. It's a more airy, more spacious presentation of the material. It throws a huge, much more realistic soundstage. You have a much better chance of having one of those outside-of-head experiences through the DX1000 than through the D5000. These are the phones for those seeking a huge soundstage without giving up the 30 Hz region and timbral accuracy (yes, the echo-y effect is very subtle, very well-calculated).
At first, I preferred the D5000. (My ears have always been calibrated for neutrality.) But, every time I A/B'd these phones, I preferred the DX1000, every time. They grew on me, and my opinion hasn't changed since. If I'm not mistaken, just about the same change happened to Skylab. He's an all-tube guy, I'm an all-SS guy, and we both love full-range phones.
Cheers,