As for stopping the spindle when the E-Stop is triggered, this code in the Signals Library of the Edit Screen WX6/ScreenLoadScript works for me:

[mc.ISIG_EMERGENCY]=function(state)
    if (state == 1) then
        mc.mcScriptExecute(inst,"m5.mcs",0);
   end
end,

With this code my Teco 7300CV under Modbus turns off the spindle with an M5 command from Mach4.

-rick