RX480: Can I Use Display Port For 4k Output And Hdmi For Audio Only To Soundbar?

This is the Hello from Aaron Janagewen.

The answer to your question is no, you can not use HDMI port to convey Audio digital signal without Video. But every coin has two sides, turn over it, you might see the queen. You can use some a dongle, such as HDMI to VGA+Audio converter, with help of it, you connect your stereo to that dongle only without needing to connect the monitor. This might provides a trade-off solution. But you'd better set the Monitor connected with Display Port as the only monitor under Windows 10 or something. OK, good luck!