How can I use the MULTI I/O section?

You can send the sound from the mixer to an external effects unit or a mobile device running an effects application. You can also change the route of the returned sound.

■ When selecting [USB] or [1/4" JACK]
When [1/4" JACK] is selected, audio signals are input/output from the MULTI I/O terminals on the rear panel in the same way as other DJ mixers.
When [USB] is selected, audio signals are input/output from the USB Type-C port in the upper right corner of the unit. This allows you to use effects applications supporting Inter App Audio on iOS devices, such as RMX-1000 for iPad. You can also use AlphaTheta effectors that support a USB cable connection.

Note: iPhones and iPads with a Lightning port won't work; you'll need to use an iPhone or iPad with a USB Type-C port instead.
First, use the [CH SELECT] switch to select the channel you want to add the effect to.
Next, turn on the [ON/OFF] button in the MULIT I/O section to use the external effects unit.
The [ON/OFF] button blinks.

For details, see the block diagram in the specifications section of the Instruction Manual.
You can read the Instruction Manual [here].