Light Machines Company Mill

can you show a picture of the stepper drivers used , and perhaps any modle number or information on them
a lot of older stepper controllers are 12v TTL and require a buffered circuit .to work with a parallel port ( such as parker ) or a simple transistor collector input
also depends on the bob your using .

if they are new drives then as Andy mentions , you tie the + side of the opto's to 5v and the negative sides become the inputs from the parallel port

but show us the internals , and we may be able to work it out for you