Walter you are exactly right. I could have just passed the signals to the drives. In fact I thought about doing just that. But heres the thinking:
This will be a project to be done in several phases.
phase 1:
pass motor signals to the drives
watch limits and disable drives if hit
report to EMC a problem has occured
LED indicators for drive status (enabled or disabled)
phase 1 will give me basic functions of my machine while playing with future phases.

phase2:
add in serial comm and set some parameters such as drive current, switch offsets, and any others I can think of. My machine has mill and hotwire capabilities all built in, I am sure There will be different "Zeros" for each. I am not sure EMC can handle that. So I may have to have my board maintain an offset and get a signal from EMC to tell it which mode its in. That way The board could adjust the axis when "tool change" occurs. for this I will need to talk to the steppers.
Until Phase 2 is complete, the offset stuff will be handled in the machine program.

phase3:
Turn the card into a full controller, being able to download a G-code program to it and hit go, elimiting the need for EMC at all.
This will be a big deal and prolly take a good while.


Happy to answer any more questions, just ask.