Thanks @wavesequencer
I had read the apple guide on this, but its taken a lot more going through both the juce apple code and also the apple sdk to figure it out.
I am at the point now where I have a class that succesfully adds a thread into an a real time thread and then into audio workgroup without having to modify the core juice classes. Its in objective-c /c++ class with a cpp header. It works by passing in the name of the device and then it searches the core audio device list itself to find the device ID then uses that to add into the audio workgroup. I’m still doing quite a bit of work to actually test it properly, and tune all the real time parameters. But I will post if the testing is succesfull. It could be adapted to work in a plugin I expect.
Thanks
Chris