What about buying them in seperates instead of kitted and getting the 20-80VAC/30-110VDC drivers instead?
https://www.omc-stepperonline.com/cl...20100%20VDC%5D
https://www.omc-stepperonline.com/cl...38%2C651.54%5D

Then drop a 500va 30-35v AC toroidal straight into them?

Costs a little more but.
You'll then safely be able to use the voltage you want to run and have the headroom not to worry about the back emf.
Prob get the setting unit to limit the current.
Just a thought.