I could get them for around 350€. I haven't checked into Ultrasone yet and before I sound like a heathen: Are they that good compared to the trio? Unfortunately MLE hasn't tested them in his awesome guide but I have heard about gaming with them or people preferring them over the trio. What's their soundstage?
I thought it had an excellent soundstage, and the positioning was spot on. I think S-Logic worked very well with my ears. The "trio" may be a much safer choice, but you might like what the Ultrasone's can do with virtual surround sound.
As for how they compare to DT880/K701's- I really can't say. I've only heard the DT880 very briefly, and I've never heard the K701. I wouldn't feel comfortable comparing them to the DT880 since there was a gap of many months between when I heard the 880's and when I bought the 2900's.
The 2900's could of been end-game for me, but I always have an itch to upgrade.