I hope I can explain this so it makes sense.

Building my rig and I have incorporated 4 "Dayton BST-12's" for the corners of the rig and one "Aura sound AST 2B4" attached to the "NLR V3 Seat Mover"

The 4 "BST-12s" are powered by a "Dayton Audio SPA250 Plate sub amp" 

The "Aura" under the seat by a "Facmoug 900" (of course)

A few questions:

How do I connect the 900s and SPA250 to the computer?

My MB supports 7.1 RCA and SPDIF (see Vantec section) inputs, but what inputs for the two amp should I use?

The 900s has Aux, USB or Bluetooth "out" so i have options there,

The SPA250 uses one RCA "out" so that will be RCA to 1/4 jack plug 

I also have the option of using a "Vantec NBA 200u USB external 7.1 adaptor" to connect the amps to the computer (this uses a USB or SPDIF to the computer)" 

If use the Vantec via the computer Soundcard SPDIF input or USB and connect the two amps to the adaptor via the 1/4" Aux out on the 900 and RCA to 1/4" jack on the SPA250 but again what two inputs do I use?

The Vantec has Headphones, Line In, and Front Surround, Center/Bass, Back inputs + 2 x 1/4" mono in inputs (which would seen the way to go) 

I have so many options but do no know where to start so I can control the output to the shakers via simhub.