Reply to Traktor Pro 2

Hello, I am planing on buying this software.
So I went to my friends house and he has 5.1 speakers.

I've tried a lot of options basicly the setup is: 5.1 speakers (3 cables going to the pc internal sound card) + my Steelseries Siberia V2 headset (USB connector - soundcard ), how do I make the sound play on both of these?