Q:
How do I set up the XONE:4D mixer, or Traktor, to record what I'm playing?

A:
To record the MIX output from the 4D, back into Traktor Pro, you need to set one of the Input Routing channels to the XONE:4D’s soundcard inputs SC7/8.
To do this, go to TRAKTOR > PREFERENCES > INPUT ROUTING and assign any unused Input Channel (A, B, C, or D) to In 7 (left) and In 8 (right).

Next, in TRAKTOR > PREFERENCES > RECORDING > SOURCE set the recording 'Source' option to Extern and select the Input Routing channel enabled in the previous step, from the External Input drop-down menu.

Next, on channel 4 of the XONE:4D, set the soundcard input selection switch UP to the MIX option and turn up the MIX Output level on the XONE:4D.
This sends the master mix output signal, post-fade, back to Traktor's recorder via the USB cable connection.

Check you can see a signal registering in the virtual meters for the selected Input Channel, under TRAKTOR > PREFERENCES > INPUT ROUTING and in Traktor’s Audio Recorder when you run audio from the XONE:4D master outputs.

NOTE:  Use the GAIN control in Traktor’s Audio Recorder to adjust the incoming MIX signal level to avoid clipping the recorded signal; if the virtual meters show red, check the XONE:4D channel input, and mix output levels aren’t too hot and, if needs be, turn the Audio Recorder GAIN level down. 

Setup the directory and other Traktor recording options as required and enable the recorder to begin recording your 4D mix output direct to the host computer's hard drive.