Microbook 2 and audio recording

[biXel]

Hi everyone.
I lurked around about my little difficulty but i did not found really a clear solution.
I just installed over windows 8.1, a trial version of ableton live.
On my system, i have a motu microbook 2 with the latest driver installed.

I can hear sound through my two yamaha monitors, but when i try to recod what i hear, no signal is recorded ( i'm using adobe audition for doing this ).
I also tried with the windows recording tool, but same result.

What am i missing about audio configuration?
Thanks.