Connection between arduino mega 2650 and two cnc shield protoneer

I need a cnc shield with 6 axes but I haven't found it online.
I saw in a video of which I attach the link GrblGru: 5-axis CNC machine controlled with Mega-5X - YouTube that the author connected two protoneer cnc shields to an arduino mega, but from the video it is not clear how they were performed links, is there anyone who can help me, maybe pointing me where to learn more?
Thank you

No link visible.

link restored, thanks