No, this is how I do it via my mixer:
Let me gusse, you don't have dj software?
You need to get a Dj software, (virtual dj) and click in their, click Config, then click and choose what your using as your setup, like this:
Now, all you really could use is another sound card , more of a top end one, such as the Creative XSound blaster ones, these are about 50pound and I use to have one and their really good, unless you want pro go for Asio
O btw you do know that you need a double ended jack and mono leads, put the double ended jack in your pc and then mono into the jack and the mono leads into the mixer.