Your servo drives will probably use an analogue voltage (+-10v) to control the motors speed and direction, if this is the case then you will need to get a digital to analogue converter for each axis. The Skyko Pixies are for this, also the Tecknix drives CPU board can do this but I am not sure if they will sell the CPU board seperately. You may also find that your servos have resolvers on them, if so then you will need to get encoders.
Hood