DDJ400 connected with extern mixer

dear community,

i will receive my ddj400 today.

Saturday i will dj for a few people.

so here is my question: when i connect my controller via cinch to an extern mixer (which is connected to the PA) which audio settings do i use to prelisten to the songs?

i used a ddj rb for a "gig" once. people could hear my music through the pa but i could not cue the songs cause there was no sound from the headphones.

it was ok at the time cause i used "sync" anyway but i beatmatch the music now so i need to prelisten.

hope my question is clear and understandable.

thanks for your help