id do as dean says- motors are small enough to replace with ac servos- ran in position mode.
closed loop isnt required- as the loop is then closed in the drives (full closed loop systems are pretty expensive to set up)
then choose a control capable of what you want/need. (governed by i/o number and working functions)
personally id go with either uccnc - due to ease of setup and working features, or kflop as i know these both can be expanded to do exactly what you want reliably. (i dont know how much i/o upgrade etc can be done with acorn re modbus capability and so on- but this sort of thing is a must if you want perfect control over spindle/ mpg etc etc.