There will be very little difference between the wiring that existing stepper drivers need, and what modern drivers will need, which is why I suggest trying them first.
Out of that second batch of photos, both circuit boards will be scrap. You can stick them up on ebay, as somebody might just so happen to be looking for a replacement, but they're not really worth anything.
Essentially both those circuit boards, are the controller. Usually there is only a single control board, but for some reason it appears that it's split over two boards.
Your first step, should be to trace all the wiring to the existing control boards. You can remove the boards, but I personally find it easier to leave them in place, draw a rough sketch of the controller with connectors and note on it where each wire goes. That way the wiring stays reasonable organised while you're tracing it, and allows for a bit forward planning before you end up with a mass of apparently random wires hanging about!
It might seem a daunting task, however you can group the wires into only a few categories -
Stepper control - typically step and direction wires, along with possibly some kind of drive active output and fault input (these may go through some of the relays)
Spindle control - again, relays may be involved, so probably best to track down a manual for the spindle drive
Machine Inputs - Usually limit switches, possibly seperate homing switches, and the E-stop circuit
Machine outputs - anything else that may go through the controller like coolant
Once you know what's connected to the controller, you can then do some diagrams of how the existing contactors/relays are wired up, and what controls them. I'd guess you're looking at a main power-on contactor, then probably one E-stop/limit switches controlled contactor. And I'm guessing there will be a relay for each of the stepper drivers, with the other possibly for the spindle or limit switches, that in turn control the main e-stop contactor and send a signal back to the control board.
It's also worth powering the machine up, and checking what voltages are available. (obviously don't electrocute yourself in the process!)
Once you've done that, you'll have a far better idea of what you have, and what you need to connect up a new controller. Then you can lable wires, remove them, and connect them to a new controller.
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