No Master Audio Out Rekordbox/DDJ400

Hi,

I get sound out of the headphones, but if I turn the pot for the headphones over to the master audio out, I hear nothing.

I am mainly going to be mixing using headphones only so this is a big problem

I already went to the settings within rekordbox software, there aren't a ton of options it's either the DDJ400 soundcard or nothing, I go for the soundcard, but still nada. what makes no sense is why I get at least sound out of the cue in the DDJ400.

so frustrating, any help would be huge!