But with this new USB/Host port on the synth, it is supposed to transmit MIDI and Audio data together, and is not registering either in Logic/Mac. In fact, when I first connected the synth, the Mac thought it was a 'computer keyboard' I was trying to connect.
That means, your computer should see both a virtual MIDI device, and a virtual audio device. Open your AMS Utility - is your keyboard listed under both the MIDI and Audio tabs? If not, install it's software it came with, the keyboard may need drivers to announce itself to the computer.