Thank you everyone. The problem is fixed!

I attached an external USB3 hub to the RB4's USB3 port, and then passed all my USB through that hub. I can now access the CEM40 mount from within Ekos. Incidentally, I also discovered that this mount has a pre-installed iPolar, something I don't remember seeing when I bought it. But all the devices can be accessed now.

I'm not sure that this hub I am using is "powered" as there is not an external power supply attached. But perhaps the use of the USB3 port provides extra power. 

Clear skies!

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