I would recommend that you go for a 4channel mixer at once if you plan on getting one in a near future.
Otherwise you have to spend money twice….
My recommendations is for a 2channnel mixer the Denon X600
And 4 channel mixer Denon X1600 (or if you want the best the X1700)
Those mixers has a very good soundcard and top quality hardware I have tested them all myself with Traktor.
In my oppinion, if you take away the SC1 and Pio and all mixers that are in the price of Pio (A&H) and all mixers that I would not recomend because lack of quality there are not much to chose from….
Here is a link to what you have to chose from all to all:
http://co.native-instruments.com/index.php?id=traktorready
The X600 is certified but NI hasnt updatet I have personaly tried it and it works…..
//DJ Hessler