I can't set [AUDIO] in the rekordbox Preferences correctly.

The installation of the driver software might be incomplete or the connection might be causing a problem.
If you’ve already installed the driver software, try again using the following procedure:

■Windows
1. Close rekordbox and disconnect the XDJ-RX3 from your computer.
2. Open the control panel (or [Start] > [Settings] > [Apps]) and uninstall [XDJ-RX3 Driver].
3. Close Windows.
4. Disconnect other USB devices, USB hubs, etc.
5. Start Windows.
6. Download the driver software from [here].
7. Install the driver software again.
　*An error will occur when the license agreement screen is displayed and you try to proceed without clicking "I agree".
8. Connect the XDJ-RX3 to another port without using a USB hub, etc.

If you still can't set [AUDIO], the problem might be caused by operating system settings, etc.
See case 3 and 6 in the guide [here].

■Mac
1. Close rekordbox and disconnect the XDJ-RX3 from your computer.
2. Download the driver software from [here].
3. Double-click [XDJ-RX3 Uninstaller] to uninstall it.
4. Close your Mac and disconnect other USB devices, USB hubs, etc.
5. Start your Mac.
6. Double-click [XDJ-RX3 AudioDriver.pkg] to reinstall it.
7. Connect the unit to another port without using a USB hub, etc.
8. Follow the instructions in the troubleshooting guide.
　macOS Big Sur: [here]
　macOS Catalina, Mojave, High Sierra: [here]
　
If you still experience the problem, it might be caused by operating system sound settings, etc.
Remove all other USB devices from your Mac, uninstall the virtual audio device etc, and restart the Mac.