Ozzy,
You are quite correct - you can assume, but it's always better to check. I did switch speakers without finding a change. I next re-did the speaker and amplifier connections. The result of this was encouraging: the left dog now came from somewhat to the right of the left speaker, while the right dog was just where he should have been, centered on the right speaker.
Now, one of the nice things about the on-screen display of the NAD T-163 is that you can easily set the db level for each channel. As an experiment, I increased the level on the left front channel by 3 db and ran the test again. This had only a minimal effect on the dog barks, but the soundstage clearly widened a bit when I tested with the Brandenburg #4.
The next thing I did was to stop eye-balling the centerpoint of the distance between the speakers and actually measure. To my surprise, I found I had been sitting slightly to the right of center. Moving over a few inches made a significant difference.
Given the difficult dimensions of the room, the center seating point is actually at the point of a pronounced Isosceles triangle - acccounting for the exaggerated effect of a slight re-positioning.
Since I can't change the room, I'll do what I can with speaker positioning (toe-in, tilting, etc.) and also see what I can accomplish by experimenting with the processing choices available on the T-163. As I once found with my original components, it may be that filling in with the rear speakers will get me closer to what I'd like to hear from my system.
Many thanks to all from me and also from my wife, who is relieved to know that the barking will be much less frequent.
Jon