Dan,
Welcome aboard, perhaps this will help.
The outputs of your breakout board are probably open-collector transistors working like relay contacts to ground rather than to the 5v rail. The link below is to the instructions for a common stepper driver from Stepperonline. Have a look at page 4 for a diagram of how to wire it up.

Kit

https://www.omc-stepperonline.com/download/DM320T.pdf