Now Playing 2 works with any controller compatible with Virtual DJ.
First open DJay Pro AI for your Mac.
Now Playing uses the NowPlaying.txt file that DJay Pro AI creates. This means the currently playing track is dictated by which track the crossfader is pointed.
Now Playing 2 will automatically pick up information as you play tracks.
If you have a slower computer, you can change how frequently Now Playing will read the NowPlaying.txt file by adjusting the refresh rate in settings.