What you have there is an excellent machine.What makes you want to change it in any way? Those aren't steppers they are high quality servos and the whole machine is built with equally high quality parts.
Has the Thermwood been powered up since you have owned it?The reason for asking is that I can't think of another way to determine which version of the software it might be running.Thermwood are quite proud of the fact that they can keep their older machines running and unless there is a really severe problem it might pay you to have a tech visit and assess the machine.
If you can get the controller powered up the built in maintenance video library should help you to do most necessary service operations.I would be surprised if any of the older controllers running OS2/Warp are still producing,but you never know.The Windows based systems can be remotely diagnosed for faults and you may be able to get guidance from the guys in Dale.