I made my decision and maybe it helps someone. But notice that amps available for you might be totally different and prices too, though I used ebay.com.
Many good amps were not available at all or they had too high output impedance or I just didn't like them small size. Often output impedance was almost impossible to find so I just had to guess.. I wanted proper volume switch etc. Even though this is my first real headphone amp/dac.
But I decided to order Yulong U100 from Asia for less than 150 euro (+customs duties which I hope to be small as possible..). Why? Excellent specs and ratings, apparently very low output impedance, simpleness and no op amp changes are even possible for me to stress. It wasn't my favourite in terms of looks and not even the cheapest. I found some other good candidates after my post as well, like XiangSheng DAC-01A which is cheaper version of Maverick Audio D1.
Then I'll make a quick comparison to all these other amps, don't get mad because I have never used any of them so I can't really know anything
But still. Objective2 is excellent choice, but should not be any better than Yulong and is more expensive and not available for good price right now. Also I dont like its front panel power cable location. Audinst, too high output impedance and Yulong should sound better with any headphones. MX2 version is better but looks ugly and still lot more expensive. Matrix Cube is excellent choice as I found it for less than 150 euro too. But Yulong apparently sounds more accurate and is cheaper too. Matrix Cubes op amps can be changed for better though. Matrix Rip, I couldn't find anything from it so I just deleted it from my list. Cube should be superior. Maverick Audio, many like it and many hate it it seems. I couldn't find its output impedance but someone said its high and it might be true. Looks very good and the chinese version was very cheap though. But its sound should not match Yulong's even after op amp (and tube) changes. iBasso, I could only find these (D4/D42) from ebay and they apparently aren't that good so I just skipped them.
And here are some reviews of the Yulong which made me order it.
http://www.headfonia.com/the-new-recommendation-the-yulong-u100-usb-dac/
http://www.head-fi.org/t/540631/review-yulong-u100-compact-usb-dac-amp
Also some guys already use it with Denon headphones and are very happy. I can't wait to test it with my Denon's as I have only used dirty cheap Asus soundcard before with way too high output impedance.