Check for loopback in the manual.

It's as simple as pushing the loopback button in the outputs where Traktor is playing <> defining the according channel as input in Ableton.
When you push loopback, the signal running at the output is present as input signal. If you loopback i.e. ADAT 3/4, inputs ADAT 3/4 will carry that signal.

Ermm, i think i got it theoretically. However, when i try to change the Output routing of Traktor from Analog to ADAT, the program crashes!

Am i missing something?

You're right. So, Traktor output is like this:

Deck A - Analog 3/4 -> Loopback ADAT 3/4
Deck B - Analog 5/6 -> Loopback ADAT 5/6
Deck C - Analog 7/8 -> Loopback ADAT 7/8
Deck D - Analog 1/2 -> Loopback ADAT 1/2

And it works with Ableton, but hardware ouput 1/2 keeps playing every other channel as well.. can't find where to assign to be just for Deck D, as it ever was...

It seems when Loopback is activated it always goes to Analog 1/2... can i disable this?

Glad you sorted it out ;-)

This sounds very very good.

So, this would be also possible for PC software playback (e.g. QUICKTIME player, Windows Media Player) ?
...want to record a video player within a browser window that comes out as Software Playback stereo channel into Studio One.

I will give it a try !