Sorry for the communications delay. I've not been on the W10 side of my partition in a while. Thanks for the suggestion about the RealTek download. It installed apparently correctly but still no sound. All the built-in diagnostics say everything is fine...
By background, my previous iMac 27 worked like a charm, 70 percent W7/30 Apple, with fully functional FS9. The computer went belly-up needing a $600 repair or... The new one doesn't accept W7, so I sprang for W10, which installed fine except for a lack of sound throughout.
Since I got FS working otherwise (and GMax, my principal time-gobbler), I'll just make "brrr" sounds when I fly.
Thanks again for your suggestion.
Sorry to hear that you are still without sound. The only other solution that I can think of is to identify the name/model of the sound card and check their website to see if there is a fix available. Also check the actual requirements for the device. If may be something as simple as it requires a certain version of DirectX (DX) for example. A fairly common issue for those who had problems with sound after upgrading to Win 10 from Win 7 or 8 was that the issue was caused by missing/corrupted RealTek files and/or a similar DX issue.
Most Win 7/8 era sound devices were coded for DX 9 but when going through the upgrade process to Win 10 DX9 files were either deleted or become corrupted. A clean install of the latest DX9 ReDistribution package (download directly from the MS website) resolved the vast majority of issues. It is worth noting that a clean install of Win 10 does not contain any DX9 files, initially it only shipped with DX10 and 11 drivers and the Anniversary update in Oct 2016 added DX12 support.