Salvaging Robot Servo Amps

I have a 4 Axis robot with DC PM servomotors and the complete drive
system. What type of input signal to the Servo amps require and how
can they be made to work with Step/Dir controllers?
Is there a simple way to bypass the original control with a new PC
control?
I want to take the motors and amps off and put them on a milling
machine (of course)
I also have a GMF Fanuc Robot which I think has AC Servos. I am
intimidated by these but am curious about converting it as well.
Thanks
Joe V