Question on hobby retrofit of TNC150 control

A friend of mine bought a Heidendhein TNC 150 controlled Wells Index
mill. He would like to convert this to PC based control, and asked me to
help.

The servo motors have what I assume is tachometers, there are only two
wires for the motor and two wires from the device at the end of the
motor shaft. There are linear scales on all three axis.
Tracing back the encoder and tach wires, both end up at the servo drive
cards as I expected. We are hoping to use the Rutex step/dir to analog
converters, and retain the servo amps/motors.

Amps are Westamp model A6514-10KS. What I take to be the inputs to the
cards are two connectors with two wires of each of the following colors
crimped to the same connectors:
red, gray, blue, purple and the other connector has yellow, black,
green. To clarify, there are two red wires to the same pin, two gray
wires to the same pin, etc.

Is anyone familiar with this model Westamp amplifier and possibly able
to help walk me through interfacing the Rutex converters?

We are trying to keep costs down, and reusing the amps/motors seems for
sure the cheapest route. The alternative is to ebay motors/amps/control
and go with steppers. But we would both like to try to keep the servos
if we can.

Any help appreciated.

Jon