Thanks. Unfortunately I'm recovering from back surgery and I may bave about reached the limit of what I'm able to do for a while since we're talking about a ceiling mounted speaker. I've now configured the receiver not to use a center speaker and have connected the center speaker to the left front terminals and moved it to the far end of the mantle it sits on. Will have to limp along like that for a while I fear, or (gasp) actually get some professional help.
Meanwhile, just for my education, I'm returning to a question in the initial post. Would it have been damaging to the amp to run it with no load connected to active speaker terminals?