I have the mill equivalent Emco machine. Most users who have the proper Emco set up seem to like it a lot, and it's only when the card or computer is missing or goes bang that they convert. I have converted (missing card).
The conversion is a wholesale rip-out of the machines electronics and replacement with new steppers, drivers, bob, PC and software. I don't think there's an option to run the Emco machine-side electronics from a modern PC and software.
Let's hope another contributor proves me wrong.