the DCS crew helped me out - thank guys, good job.
If anyone was having the same problem: 1. go to AUDIO, confirm "main audio out" and "headphones" are correctly selected. I had two options with SteelSeries Arctis Pro: GAME setting and CHAT Setting. I had previously been set to DEFAULT which was not working any longer. I moved it to CHAT, still not working. When I moved it to GAME it worked.
Lesson - if you are more of a USER than techie (hand raised here) then don't despair, the guys at DCS will help - so reach out if you cannot resolve it yourself.