Being a glutton for punishment I messed around with this thing again. I reinstalled Mach, told the smooth stepper how to behave, pulled every chip off the C23 board and re-seated them while putting the newer set back in and fired it up. I have my axis back and control of the VFD speed via the analog output. My M3 and M4 commands are still not triggering the relays...well, one is still dead.
Interesting thing...with Mach opened, when I power on the C23 board pin 16 and pin 1 activate. Pin 16 triggers the associated relay. Pin 1 relay is dead. Once I input M4 pin 16 relay switches off as it should but will not switch back on (as it should) with an M3. Pins 16 and 1 do not re-activate as if M3 and M4 commands get lost in the ether.
Spindle is set to step/dir
Disable spindle relays box is un-checked
M3 is Output 1 and set to pin 16 port 1
M4 is Output 2 and set to pin 1 port 1