The plates that we use are designed for BK-LFE minis and advanced BK4-4 buttkickers. The pre-drilled wholes are to fit those units.
You may want to get some plywood, cut about 18"x6" pieces and bolt them on the bottom to the metal frame of the chairs. You can use some wholes that are on the frame, and you may need to drill a few more to mount the plate. Then you can install the transducer on top of that plate.
Some people mount the Aura shakers to the bottom of the seat and used heavy duty wire ties to do so. This is the easiest way to do it.
Fusion Collection Seating
Ultimate Home Entertainment