Hi Craig,
I have a AKZ250 and have just replaced it with a ESS. ( not fired up yet...)
I agree....I think you will be better off not using the TB6600's. No experience with them but from what I have read. They can be problematic.
I don't think the AKZ250 can 'slave' a second stepper, but you *may* be able to drive 2 drivers from the same signals. I guess you can try it and see.
The Enable inputs are not needed, from my experience.....just need the 4 control wires.
Have you got the Mach 3 plugin for the AKZ250?
I also soldered in another 3 pin connector at J12 so I could use a 2nd pot. Semed to work ok, although one indicated 150% when at mid travel. ( seemed unusual as I expected 100% )
I didn't bother persuing it further.
Steve