You should be able to build a PREEMPT_RT image using Armbian for the OrangePi and install LinuxCNC and XFCE on it. I have done this with a Odroid N2+. I would go that way and ditch the PC out of the equation.
In the build process, you just need to run menuconfig to configure the PREMPT_RT flags.
Start here
docs.armbian.com/Developer-Guide_Overview/
