External Soundcard Advise

Hi guys,

I am looking at buying KRK Systems RP6 G2 Series Rokit Powered Monitors [http://www.soundz.co.za/pKRKRP6G2/KRK-Systems-RP6-G2-Series-Rokit-Powered-Monitors-pair-SPECIAL.aspx]

Also I have a DJM350 mixer and I want to connect it to the monitors.

I use a Laptop and want to know what kind of external soundcard I need to buy ?

Thanks !