DDJ-FLX4 Master Output dropdowns empty in rekordbox - no sound through speakers

Hi,

I have a DDJ-FLX4 connected via USB to my Windows laptop running rekordbox 7.2.14, but I cannot get sound through my external speakers.

The issue: when I select DDJ-FLX4 WASAPI in Preferences > Audio, the Master Output L and R dropdowns in the Input/Output tab are completely empty — there is nothing to select.

What I have tried:
- Unplugging and replugging the USB cable
- Trying different USB ports
- Uninstalling and reinstalling rekordbox
- Restoring default settings in rekordbox
- Changing the Windows audio format for the DDJ-FLX4 to 4 channel, 16 bit, 48000 Hz
- Uninstalling the DDJ-FLX4 from Device Manager and letting Windows re-detect it

Important notes:
- The DDJ-FLX4 is recognised in Device Manager under Sound, video and game controllers
- The DDJ-FLX4 tab appears correctly under Controller settings in rekordbox
- VirtualDJ works perfectly with the same setup and speakers
- Windows Sound Settings shows the DDJ-FLX4 as the default output device

It seems like rekordbox cannot map the audio channels of the FLX4 even though it recognises it as a controller. Has anyone experienced this or know of a fix?

Thank you