Start project with 6 axis Nema 17 stepper motors

Get the LinuxCNC ISO from the downloads page, write it to USB, boot the PC from it, install it to HDD, reboot.
Make a config for XYZA, wire drives to BOB (beware it does require 2 of 5V power supplies if you need isolation, only one if no isolation is required), see if stuff moves around.
Another thing to be aware of, the BOB uses really slow optocouplers, so might need to use a very slow base period, at least 100000.

The installation description was added for completeness since it was not clear that you already have LinuxCNC installed, so disregard.

Use the PNCconf tool to create a configuration for a XYZA machine as it does not let you create a 6 axis configuration. You then need to modify the created hal and ini files to change the XYZA to XYZABC or whatever you need.