Hi Brian,
We are working on documentation and more sources of information like a jBPM5 book, but it's all work in progress.. I would like to help you to understand how components interacts in the mean time.
If you take a look at the MinaTaskServer, I think that will be easier for you to understand because it's a plain socket communication based on messages.
The HornetQTaskServer works in the same way but adding all the advantages of using a JMS client/server. You will get message retrying, message reliability and Queues clustering for free. Depending on your requirements you can choose the Mina Server or the HornetQServer, or you can implement your own transport to fulfill your requirements.
I will be glad to help you and I'm also will start writing some post about those topics with examples. Thanks for the feedback and if you have doubts or if you find issues let us know!
Greetings!