Thank you so very much, fine folk.
Sorry I was away for several hours yesterday evening and night.
I hade done something even more basic than most of you guessed or surmised. I had the main speaker connected to the Height input rather than the Main. In hindsight this makes absolute sense, duh!, but the single pair of (Height) connectors lured me to mis-wire the speaker.
Thank you all so much for weighing in - fabulous community for folks like me - obviously in over their heads - have great days.
Bruce