I don't get why the video renderer affects your sound? Is your audio coming out of your graphics card?
Anyhow, if dkeeton's suggestions doesn't work, try these:
In RA2'S opening menu, type 'hires'. You should then hear a beep. Now go to options and you should have more screen sizes to choose from. See if any of the new ones fix your problem.
In Win10's Settings -> Display, make sure that 'text, apps and other items' is set to 100%.
In ra2.exe's properties (or whatever file you use to load up the game), click 'Change high DPI settings' and play around with the settings there (don't forget your original settings incase you have to change it back!).
In CnCNet, try Windowed Mode -> Borderless Windowed Mode
You mentioned that using ts-ddraw, then changing to cnc-ddraw, then going back to ts-ddraw worked but disabled your sounds (which is frickin weird ); while in-game, alt-tab out to Windows then have a look at the Playback devices and try a different device (again; don't forget which device you're using before changing it!)