Relevant links:

RMAA: Onkyo DP-X1 24-bit single-ended and balanced — ohm image
RMAA: Pioneer XDP-100R 24-bit — ohm image
RMAA: Astell&Kern AK70 24-bit — ohm image
RMAA: Astell & Kern AK70 Kai (Ryuzoh mod) 24-bit — ohm image

This thing sounds good. Real good. It really fits in a front pocket. I has a real hold switch. And a damn fine balanced output. That it costs just ~350$ in Japan and another Benjamin abroad is shocking. 

Why didn't I listen to it? Simple: I don't care. The DP-X1 is too big, too awkward, and too slaved to an unfathomly music-unfriendly and ugly interface that I would never consider owning it. It feels bad in the hand, and whose interface relies more on glitz than it does on gravitas. Getting music to register to it was even more difficult than for the Astell&Kern AK380 (RMAA'd here - reviewed here), primarily because it is new and its firmware doesn't do ID3 tags well.