Baldor top cards with the green or orange 7 segment LED have a 16 way IDC header which 'taps' into the step and direction signals for axis 0,1,2 and 3
This means that any, or all of the axes can drive external stepper drives rather than the 3 fitted to the base board.
NB, Some earlier RS232 only nextmove ST boards didn't have the connector fitted, just soldered holes.