That did it; thank you.
I think this should be clarified in the documentation. Though yes, it does say TCP port, I wasn't aware that there were separate ports for the webserver and some other service. A webserver runs over TCP, and the JSON-RPC service runs over the webserver (or at least it can -- I use the webserver port in some of my JSON-RPC scripts), so I assumed TCP port meant webserver port.
It might also be nice to provide some better error logging. As I said earlier I did have a debug message saying Hyperion had connected to Kodi, but then obviously nothing was happening beyond that. Some messaging here saying it's not getting responses, or bad responses, or whatever, would have helped debug.