I bought ue900 and am disappointed.
Even for the price I bought them for (169 pounds), they don't sound that good at all. I find them boomy, bloated, too bright (personal experience of a non-audiophile). I've been tinkering with equalizer and used different tips (the ones supplied with IEMs as well as sony hybrids).
Couple of years ago I had RE0 which were far superior to the UE900 I have now (ridiculous, I know). They were clean, the separation was amazing, and most important of all - the clarity was top notch. My only gripe with them was the lack of bass.
Now, I might return the ue900 if I find a decent substitute. My upper limit is 250 euros, unless I find a mind blowing set of headphones for a bit more.
What I'm looking for is something like the RE0, but with more bass. I heard that RE400 and RE600 improved in that aspect - the RE400 currently stand at around 100 dollars, which is amazing. RE600 are unfortunately too expensive at 400 dollars.