Hi there all,
im owner of an DX90 for ~14 days now, purchased by eglobecentral, a seriously strange shop in Europe but everything works fine and the ibasso reached my place within 7 days (~300€).
I used the Ibasso with the following headphones for now. Shure 535, Bosse QC15 and standard Nokia Lumia 920 in ears which came with my older Lumia 920.
First, I must say that the sound is okay, but its almost similar to an 95€ used Lumia 820 - which offers the far better player interface (Windows Phone), in terms of responsiveness and over all handling. The DX90 behaves strange from time to time. Overall I would say it reacts quite fast, but it also tends to hang seconds from time to time.
Believe it or not, but the bundled in ears of the Lumia 920 head up with the Shure 535 in terms of soundquality. Listening to Pink Floyed - The Wall album in FLAC, im kinda disappointed of the DX90 + Shure 535 combo compared to a Lumia 820 with bundled in Ears, wired...

- in addition the Win Phone EQ is far better than the ibassos (I disabled it for the ibasso usually as the SQ drops simply enabling its EQ in my mind)
Even if I do a complete zero on the EQ it looses pressure and clarity ... so strange...
Im missing some deeper bass and pressure on the lower end in the DX90 - which greatest advantage is the output power on headphones. The QC15 delivers the best pressure compared to all 3 headphones, even if its called not to have the best audio quality at its pricerange. (even if im not listening to drum and base, usually i listen to classic rock or the usual top100.)
All over, I prefer my my Canton + Denon Setting at home at higher volume.
So far my impression.
Regards
Edit: another advantage is the line out, which provides the ability to use 2 headphones with the DX90. I bought him as my gal is a singer (marcella-carin.de) and the DX90 is almost perfect to replace a standard CD player for the half-playbacks... with 3 hardware buttons |<< |> >>| ... + Line out to use with her dual Bose L2 System.