How do you rate the motion of the UC400eth? I think earlier you wrote that it was decreasing run time significantly, like 20% or so. I noticed that the CNCDrive folks are not particular about computer horsepower which is a good thing in my book.
As I mentioned before, there is one minor issue, but if your machine has decent accel rates, you should find it to be much better than Mach3. While it may not be faster running identical code, it will generally allow you to run at faster speeds. The vast majority of people that go from Mach3 to UCCNC find it to be much better. And with all CNC Drive controllers, you can still run Mach3 if you wanted to , as they support UCCNC, Mach3, and Mach4. (Mach4 support may be limited).
Here's a comparison between UCCNC and Mach3 doing 3D carving. https://www.youtube.com/watch?v=UJ8NM1MVFdM
Again, the main thing you need regarding PC support is OpenGL. The onboard graphics of most modern Intel processors should be fine, though.
I am thinking that all I will need to do is connect the cable from the UC400eth to the back of the G540 and plug the UC400eth into the ethernet connection and be good to go. Sure hope so, because if there is one thing I do not like doing is wiring.
I think you'll need a small 12V or 24V power supply for the UC400ETH, but yes, just plug the G540 into it. And you have the option of adding a second breakout board if you want/need more I/O.