Happened upon another post with a similar issue, the board he linked looks like the camxtool I’ve been trying to use. Dual y-axis belt drive He had the same initial confusion about the secondary Y axis controller.
I think I’ve figured out the controller plug slots on my benbox should be labeled X, Y, Y2(labeled as the reverse A/B+/- of the rest), Z(unused). So if I can get the S-+ slot to run my laser I’ll be set on the hardware side. On the other post it sounded like GRBL can handle this setup with the Y2 - would it be the cloning mentioned? So this setup is my goal, I’ll be googling how but welcome further help from search terms to how-tos!