My Goal:

To be able to use one of the USB Ports on the back for Carplay and the other for App Radio.

I've just installed the 8100NEX in my car.  I followed the install instructions and I'm not getting the results.

My setup:

USB 1:  USB extension (included in box) to a lightning cable to the phone directly.  Working fine for carplay.

USB 2:  Lightning cable paired with the HDMI both connected to the Apple AV adapter.

So, Carplay works perfectly.  but when connecting to the other lighting: nothing.  

Any help?

Both CarPlay and AppRadio Mode need to use USB 1. I don't think it was ever intended to allow users to swap between modes very easily (without swapping connections).

Hint: Even if you do change connections, I've noticed that an iPhone must be rebooted when you change from AppRadio Mode to CarPlay and vice versa. Otherwise you get weirdness. Somebody else here has had the same experience. This makes switching between modes even less friendly. It's more of a choice you have to commit to rather than something you can switch between at will.