Native Instruments offers an ideal bundle for mobile use of TRAKTOR DJ Studio 2.0. The TRAKTOR Bundle includes, along with TRAKTOR DJ Studio 2.0, the Ego Systems USB audio card GIGAPort AG.

Extended information

Thanks to the individual outputs and the ASIO 2.0 drivers, the GIGAPort AG works perfectly with TRAKTOR DJ Studio 2.0. The outputs can be individually assigned in the TRAKTOR setup menu.

This way you could assign TRAKTOR’s master output to outputs 3 and 4 on the GIGAPort AG, and route the monitor section through outputs 1 and 2 (and this way through the headphone out as well).

Or when using an external DJ mixer the stereo output of TRAKTOR’s deck A can be sent to GIGAPort outs 1 and 2, and the second stereo pair from deck B to outs 3 and 4. Conncet these outputs to the two stereo line inputs of your DJ mixer, and you're ready go.
It’s really up to you – and with this software/hardware combo the possibilities are looking pretty good.