This article will teach you how to "hack" your mac's internal soundcard so when you are having a mix you can send the audio output to your computers speakers without having to use one of these:
Note: you will not be able to monitor with headphones when using the aggregate device.
1. Connect your controller to your computer via USB.
2. Click on the spotlight search and type in "Audio Midi Setup" and open up the Audio Devices Window.
3. Click the "+" symbol in the bottom left corner and then select "Add Aggregate Device" .
4. Once you have created an Aggregate device it will show up in the menu alongside the MIDI controller that you have connected. Rename the new device by double clicking on its name. Make sure it has the exact same name as your MIDI controller.
5. Now in the right hand window select this device for use as a "Built-in Output". It's very important you set the aggregate device to 'Built-in Output' otherwise you may experience issues running Serato DJ.
NOTE: On some newer versions of macOS, Built-in Output maybe referred to as Macbook Pro Speakers or Built-in Audio like in the example further below:
6. Now open Serato DJ, you should be able to have a mix with your controller and all Audio will be played via the Internal sound-card on your Mac!
NOTE: Make sure to delete the aggregate device from the list when you are done mixing so next time you connect your controller Serato DJ recognizes the controller as the soundcard to be used. To do this highlight the aggregate device that you created and remove using the "-" button in the bottom left corner of the audio setup window.