Reply to Soundcard Problem

Hi!! I'm buying a new DJ gear , a Novation Launchpad, a M-Audio Oxygen 25 3rd Gen and a M-Audio XSession Pro, also I own yet a Hercules Mp3 e2 and a cheap USB Soundcard that I use for prelistening, but the people tell me I need a properly DJ Soundcard if I want to use that all hooked to Traktor (actually I use VDJ 7 Pro), I don't have a big understanding on technical stuff but the Soundcard it's only needed to sync a mixer to the computer and to precueing and maybe to use to mic and actually I have all this features, haven't I? sooo... do I really need a Soundcard? please help me!!