Reply to Connecting traktor with CDJ 850/1000/2000

Hello everyone,

I've been DJ'ing for a while with midi controllers, such as hercules RMX, Traktor S4, ...
But now I'm going for a pioneer CDJ 850,1000 or 2000. The thing is a lot of people are telling me different ways to connect a pioneer with your laptop ( especially with the software Traktor ). I've been looking around for tutorials, information from users that have pioneer and I got pretty confused of how you set up your pioneer with Traktor. The thing is, I would really like to have my laptop connected to it, so I can have a better view over my tracks. Many people so far, have been telling me that an audio card is a must. But then someday I've seen a tutorial on youtube, where a guy shows he is just running his laptop with the CDJ 1000 mk3 and it is without an audio card, directly connected to the laptop and he can perfectly mix.

So my question is, is an audio card needed, or how do you guys connect your laptop with a pioneer?
Do you also need a special mapping ?

I would appreciate to have some information !