Proper Setup Question

Hello. Unfortunately, a friend died and left me tons of stuff that I need to set up. I alreadyhave a Yamaha S90 Keyboard. He left me an MR816x, a Mac laptop with Cubase (maybe it’s Nuendo, I have to check), and tons of keyboard software. I see the recommended setup in the Steinberg Manual, BUT, the Mac and S90 need to communicate so that I can control the much superior sounds in the Mac.

Does anyone have a diagram how I should set this up so that everything communicates properly? As an aside, I’d been using a Behringer 816air for live gigs and home use. Also, should I abandon the Behringer and use the 816 as a home mixer? Is there an advantage to keeping the Behringer in the mix?

Thanks everyone!