Retrofitting a 3-axis VMC with DC servos - guidance needed

7I73 is an lcd/matrix and io expender so you may need voltage shifters  for some of the pins. If your are not planing to use lcd/matrix keypad  Then I would suggest you get  7I84U, the i/o's are 5 to 28v tolerant. four input pin voltages are readable with 8 bit resolution.  Two MPG encoder inputs are provided as an option on four  field inputs

Hello, sorry for the late reply; I've been dealing with some personal matters.

I finally decided to go with the 7i97T and the 7i84U. I also bought the 7i74 and the 7i73 for future expansion. The first two boards alone are already overkill for my current needs, but I got the 7i74 so I can eventually add the 7i73 for a pendant controller with a screen.

I'm thinking of setting that up from the beginning since the PC won't be very accessible once everything is running. Having a handwheel for moving the axes and a few shortcuts or macros seems like a really good idea.

With just the first two boards, everything should be up and running. I expect that counting shipping and everything else, it should all arrive here in Argentina around the 15th of September.

So now, I'm starting to look for the PC to run it all. I saw the HP Z400 that @tommylight recommended for @andy. I can find it here for fairly cheap, refurbished. It comes with an Nvidia FX3800 for video output. Is that a good PC for this use case, or should I be looking for something else?

Thank you guys for all your help.

Z400, Z420, Z600, and probably Z440, Z620, Z640, Z800, Z820 should all do just fine, those 3 at the start i have tested over 20 by now. Also HP 8300 SFF are pretty good, i have maybe 6 or 7 in daily use on machines.
Dell Optiplex series are also good, 7020, 9020 and 980, these i have in daily use, several of them for several years, but they do tend to heat much more than HP ones.

Finally, after a long wait, the boards have arrived! Now I'm looking to buy the PC to control the machine. Checking all the models you shared before, I couldn't find any of them available in my country for under $700 USD.

However, I found two options: a Dell Optiplex 790 with an i5-2400, and another refurbished PC with an i5-4400 (the seller didn't specify the exact model, just that it could be an Optiplex, HP, Lenovo, or Bangho).

Which one would recommend? Both rely on integrated graphics. Is that going to be an issue in my case? From what I've read, a dedicated GPU is usually recommended, but I'm not sure if that's only for software pulse generation or if it's recommended for hardware-assisted setups too.

Thanks in advance!

Dell Optiplex 790 is still usable but needs at least 4GB of RAM.
Lenovo M93 with 4000 series CPU are also good, so if this is what you can get it is better than that Optiplex.
Fujitsu from that era are also OK.

I've never used anything other than integrated graphics. no need for a seperate GPU