Craig
Of course CSMIO recognises OSIG_ENABLE0 - I use it to enable Motor 0. I think the issue you were having may be a conflict with the core, as the signal was changing in response to Enable/Disable, as it normally does.
Though Mach's LED reacted in response to OSIG_ENABLE0, it would have been interesting to know if the LED on the CSMIO itself also reacted, proving that the command was reaching the controller.
Though the CSMIO is not perfect, it performs very solidly on the basic functions such as I/O.
Allan