You need the Pulseaudio Volume Controller
Using Terminal type in sudo apt install pavucontrol
Then go to Sound and Video in start menu
You will see Pulseaudio Volume Control
Open it and click "all output devices" lower right
On the top of menu
Input Devices- Monitor of HDMI audio
Output Devices-shows HDMI
Keep arrowing to the right to "configuration"
Go to Profile- in drop down hit HDMI PORT Digital Stereo
Now.....try your sound--it works!
