If you are referring to this thread: http://www.head-fi.org/t/620938/new-denon-music-maniac-urban-raver-lines-d7100-d600-d400-c300-appreciation-thread
It's about all the new Denons: D7100, D600, D400 & C300. I've been through that entire thread, and most of the talk is about the D7100, and D600. Not much in there about the D400... so I specifically chose this thread to reply to since it was specific to the ones I am most interested in... though the D600s might be an even closer comparison with the Ultrasone Pro 600, their newness has the price out of my range... in fact the D400s are still retail most places... and the Ulstrasones are going for the low $300's now.
My only reservations about the Ultrasone's is the harshness of the highs. But most everything I read still puts them at the top of the list for massive, deep, controlled bass... and that the highs do tame a bit after burn-in.
From my reading in the other thread, many people are putting the D600 up there in the "harsh highs" realm too, which is still a turn-off, and they are almost $200 more than the Ultrasones if you're talking street price and not retail.
But the few posts I have read about the D400 sound like I might like it's sound signature best... however the onboard amp seems more of a con than pro... especially if you want to get many years out of these... which I would. I assume once the battery dies they are useless without an expensive repair... I doubt they work at all turned off... but it would be nice if they could perform as "normal" headphones with the power off.
But my biggest question is still if anyone can comment that has heard both the D400 and Pro 900. How does the bass compare, and are the D400 warmer and less harsh?