I took the car into Best Buy once again and the tech, who is very good, I think, diagnosed it immediately as needing a "hard reset." This means he pulls the system out, disconnects power and plugs it all back in again. That solved the problem. This is the second time this had to be done and it occurred to me that I could accomplish the same task by disconnecting the battery. Cost to me: $54.
I'm hoping the issues with the Pioneer will calm down over time, but I doubt it. I may just need to be happy disconnecting my battery every six months or so.
Slicing my throat on the cutting edge of technology.....