Not really sure if you would be able to keep anything but your motors are well within the voltage for Geckos, CNC Teknix etc drives. You will need to find out the current requirements of the motors to determine if indeed you can use Geckos or Teknix.
If your original drives are OK you can probably use them if you get digital to analogue converters such as the pixie boards.
You will really need to find out the info on your encoders, find out their count, or for that matter whether they are actually encoders as they may even be resolvers.
Hood