Our Furrion TV and Stereo is connected via the AVI Input on the Stereo.
Select AVI on Stereo and then adjust both sound settings on TV and Stereo.
If that does not work you should check if you have a Audio Cable from the TV to the Stereo.
You can upgrade with Furrion Speakers if you want to stay with this vendor:
https://www.furrion.com/store/audiovisual/audio/
Mike