UART is the preferred way to go
it can be done via USB as well as RS232 and RS485
add UART comms to daemon, extend parameters and check communication between axiom remote and daemon.
The PIC32 handles the low level stuff and the electrical interface
On top of that to use UART over USB (or HID, which might be interesting too) on the PIC32, the USB stack needs to be implemented.
http://ww1.microchip.com/downloads/en/DeviceDoc/60001191G.pdf (section 11)
So the suggested steps would be something like:
1) plan what PIC32 based device(s) are realized via USB - any development board with the PIC32 works
2) make a test setup with Harmony (Microchips USB Framework) to see how/that it works
3) adapt this to work without the Microchip libraries/framework