Hi Emmanuel,
the code should still be available from the link I posted
here: https://drive.google.com/file/d/0B27_4JL_xnCqRUVIcXB3eEY5Vmc/view?usp=sharing
the archive holds a (slightly modified) version of ofxNiGrabber2 already.
and you can copy the extracted folder to the apps/myapps folder within openframeworks.
and follow the instruction in the readme, otherwise you can only run the app as root.
Unfortunately I did not own the xtion and had to return it. So I can't help with debugging or extra features at the moment.
Good luck..