My issue is resolved.
My issue involved the Creative Sound Blaster Apps not functioning (particularly Wave Editor 7) under most recent Windows 10 build 1903. Windows x64 Pro, Audigy Rx sound card.
I rolled back to 1809 and still no functionality of the Creative apps.
I uninstalled the Creative drivers and apps completely, using Revo uninstaller.
Still running Win 10 1809, I attempted reinstall of Creative apps. The installer would hang at 79% (while installing drivers).
I repeated the uninstall of Creative products using Revo-tried installing again-same hang at 79%.
I used Windows admin shell to run SFC (system file checker), and found some corruption! This was a little hard for me to believe, having recently fresh installed and everything running smooth and up-to-date.
At this point, I ensured that Creative drivers and apps were completely off the system (again), even going through advanced mode with Revo Uninstaller, looking for any registry entries for Creative apps. Once satisfied, I re-installed Windows 10 build 1903. The process found the Sound Blaster card (Audigy Rx) and installed a driver for it automatically. System sounds were functioning OK, so I took the chance to install the Creative apps... everything works now as expected.