Audio sink option

[PJThys]

Glad with your app.
I have a problem with audio sink.
I have a Oneplus Nord 3 with android auto. I have an old tablet (Samsung SM-T280) with lineage 14 (android 7.1). Android auto is displayed nicely and correct on the tablet with the help of the Wireless helper app..
I want the audio played on the tablet, and through the tablets audio jack plug to the car's media-system AUX. Whatever I try, both sink options always play sound via phone, which has no audio jack and not on the tablet.
So either I connect the phone's usb to an usb-audio jack cable (which works) but I cannot load the phone, or I connect the loader cable to the phone and have no aux.
The tablet has both Micro-usb for loading and jack output for AUX input in the car.
The sound on the tablet in standalone mode works fine with the aux in the car's media system. But if I start Headunit, it switches to phone. The car has no bluetooth for audio, only for handsfree calls, so bluetooth connection to the car media system is not an option.