The HDJ-2000 do have a great groove factor, which gets even better with some easy modding. They have a downplayed treble though, which does not play as well with acoustics. It sounds fine for the most part, but doesn't have that "zing" in the upper registers to really bring the strings and horns forward (personally I'm overly sensitive to these high frequencies, so that's fine by me).
The D2000 do indeed have a nice grooviness to them. A more laid back sound, not as much punch but deeper extension and rumble, like the Pioneers took a good long drag of "the good stuff" and are mellowing out. I don't know if it would induce more toe-tapping in you, although they do have a more level treble than the Pioneers so that may work for you.
Thank you for your reply. From what I understand the D2000 would be somehow more 'mellow' although more correct and hi-fi sounding. The treble rollof in the Pioneers is ok for me (even very loud from an iphone they were never ever agressive!) but if I could change something I would like some more mids... and I think that's not the D2000 (proeminent bass&highs).
If you had to pick one for listening to fast, rhythmic electronic song (be it house or whatever, but not chillout) would you pick up the Pioneer or the D2000.
And for using straight from an ipad/iphone out, which would be the easiest to drive?
Finally, regarding isolation from outside noise, I believe the Pioneers are better than D2000, is that right? much better?