impossible to play music files located on laptop to qnap connected to DAC

Hi
I have a QNAP HS251+ connected to a DAC through USB.
I go through my LAN
I have installed both program on QNAP and my laptop OSX 10.12.6
I see the driver in the system preferences/ sound : when i choose it, nothing goes through.
Same issue when streaming internet radio through web browser
1. Any idea how to achieve this ?
2. What could go wrong in setup?

Thank you very much for your help.

Best

GdeM