This was going to be a call for help but I solved the issue but in doing so could not find anything to point me to the solution so I'm posting here incase it can assist others.
I just bought a new PC with a ROG Maximus XII HERO (Wi-Fi) motherboard. I spent 2 days trying to get the NDI Screen Capture to work. Video was fine but no sound.
To fix the problem I finally uninstalled both Sonic Studio and Sonic Studio Virtual Mixer, which are auto installed with the motherboard drivers, and then everything worked just fine.