Where does it peak. On the master or on one of the faders? In Traktor the main only controls what comes after the fader. If you play a track and the vu meter of that channel peaks then you should turn the gain down. If that track peaks on the channel it’s vu meterĀ evenĀ with the gain at 0, that track might be really loud. Try it with different tracks.
The gain is not a setting that you only set once. With each different track you have to adjust the gain to make sure the track does not peaks. But some tracks can be recorded really loud.
Let me know how it all works out