Rekordbox with ddj 400 using soundcard

so im looking at getting a soundcard ie focusrite 2i2. How would i set it up ? would you run RCA to sound card and then sound card into laptop.

or is there a way to get the sound coming from ddj 400 from rekordbox into sound card with using RCA. like can i change the outputs on rekordbox so it goes into the soundcard?