I have started looking at how to enable discovery today. In the process, I have discovered that the base port is now 9300. I changed the fixed value in the plugin and I have now got it working again.
I have uploaded a pre-release (using port 9300) to Github, which is available here:
Roon Controller - Version 0.0.39Download the Roon.indigoPlugin.zip and double click it to reveal the plugin and then double click that plugin file to install.
You may get a message about unrecognised developer where it asks you whether you want to move it to the bin or cancel; reply cancel.
Then go to Settings > Security & Privacy, unlock the pane and then authorise the plugin (open anyway)
Then in Indigo, reload the plugin and reply Open to the prompt and you should be good to go.
You will have to have Roon > Settings > Extension open to re-authorise it.
Let me know how you get on.
In the meanwhile, I will continue investigating how to make this more bullet proof by utilising discovery.