Can you use a mic through the Kontrol S2?
Yes. You can use a microphone with the Kontrol S2. All you have to do is plug the mic into the Mic jack on the back of the S2, click the "Engage Mic" button on the front panel and then set the gain using the knob in the back (right next to the mic jack).
When you want the mic to be silent you just click the "engage mic" button again.
It's important to note though, that the S2 does not provide the same flexibility as the S4. For example, you can't assign the mic jack to any of the decks in Traktor. It's essentially just a line-in that gets routed into the master output of the S2.