If the existing servo drives work (technically they're Servo Amplifiers, and a search should turn up more options) , keep them. You'll just need to figure out what they are, and what signals they need to run (they'll be +/-10V analogue drives, but you'll need to find enable/fault signals).

Other option is you convert to something like the CNC Drive DC servo drives, which will accept a step/dir signal, removing the need for an analogue controller.