Sorry, I didn't get a reply alert.

The problem seems resolved, though I actually don't know how. I am using a serial adapter. At first, the port was just solid red and unresponsive, but in all my tinkering, I must have done something that made it happy.

So it's working....now I'm just going through Sony support purgatory trying to track down a command list more recent than about 5-6 generations ago. (Honestly, I've never seen a manufacturer so poorly support this feature!)

Thanks for the reply.