It Depends how many Channels you are wanting for a basic 2 deck set up using Cdj's you would want 4 channel 2 per deck 1 master out and 1 booth so you can hear it through your head phones but if you were doing Karaoke you would want 6 channels for 2 microphones all going 2 the master out. but it changes again if us software and controller because most software has an internal and external mix mode. Here is a video that might help
It Depends how many Channels you are wanting for a basic 2 deck set up using Cdj's you would want 4 channel 2 per deck 1 master out and 1 booth so you can hear it through your head phones but if you were doing Karaoke you would want 6 channels for 2 microphones all going 2 the master out. but it changes again if us software and controller because most software has an internal and external mix mode. Here is a video that might help