The upstairs dog has been much quieter since Wednesday, barking only occasionally (and going totally nuts when its owner gets home). I was bracing for a long season of barking, so I am relieved and somewhat surprised. Maybe the dog is more used to being alone than I'd thought, and it was just going through the adjustment to a new home.
Meanwhile, our dog seems only barely aware that there's another canine creature in her vicinity. The only real indication I've seen so far: when we go out into the back hall on our way out for a walk, she has started turning her head and sniffing up the back stairs. I'm sure the two dogs will meet eventually, but I don't harbor any illusion that they will become playmates, because our dog has little use for other dogs beyond sniffing them.