Well here's something:
Outlook: DT880's outlook is very fine and they fit comfortably to my big head. Build quality is very good and I like the material (aluminium). They also look valuable and definitely better than 650.
And then the sound. I like it! I like it much more what I did on first time when I auditioned them at the store with a whole different equipment than I have.
Details/speed: I was amazed about the amount of details even at the first time and I still am. It's just something great I think. 650 gets beaten 6-0 by 880 in this area. You really can hear every little detail that has been recorded. There's one problem though. If the record is poorly mixed it sounds poor with DT880. They are totally unforgivable. And speed. DT880 is very fast. When listening to Steve Vai's hardest guitar solos I find them much more enjoyable with 880 than 650. Some songs by Vai might sound little muddy with senns.
Soundstage: Aah the soundstage maybe the most important thing when I'm choosing my headphones. It's great with DT880. It's even little bit wider than with 650 and you really can feel the space around you. DT880 is really strong in this area. I won't even compare them to Grados by this matter when there's is really nothing to compare.
Brightness/highs: DT880 is much brighter than 650. Not even near of SR225 (which I also have at home now) and that's just good thing. There's just the right amount of brightness in sound. It doesn't strain when listening for long periods. DT880 also extends nicely on highs but doesn't get harsh.
Bass: Well as you may know this is the poorest area of DT880 and at the same time weirdest. After my first audition I thought that there's no bass at all in DT880. That's crap. The bass is there but it's somehow hidden. This is really hard to explain. With some tracks there's strong clean bass, maybe even better than with 650s but with many (too many I think) tracks that 650 plays with nice deep and fully bass, DT880 just has no bass at all. I find this very weird. I think this depends of mixing again. DT880 is just so unforgivable for poorly mixed records. But I must say that DT880 can go very deep if it wants to.
After all I think DT880 is very good headphone and it would compliment my 650s very well but I would so much like to find the one and only headphone which would do it all. Now I'd like to find headphones which work well with rock and I think DT880 is better for this area than 650s. I'm really considering of buying a pair of these beauties.
EDIT: Added something about speed.
