Hello.
This knoweldge base post on NI’s web site shows how 8 wire stepper motors are connected internally and two different connection methods (parallel and series) that allow them to be controlled like a standard 4-wire bipolar stepper motor. We do not have an Arduino library for controlling stepper motors from the VNH5019 driver, but this code posted by Jeremy on our forum might be helpful as a starting point if you want to write your own.
-Nathan