Just going by your 192" size I personally think 4 more aura's would work.
I had a 7 ft couch (84") and 4 shakers were plenty. but 96" each way is a lot of area to
cover, although it is more than twice the size of the couch I had by 24", 4 more shakers would be fine.
Don't know about the corner area you talk about.
I have no experience with Buttkickers. Also IMO hard wood is not the ideal wood to use.
It's strictly a matter of taste. I think 1' X 6" pine would be fine....transmits energy better.
If you go with the Buttkickers, I would contact the seller/company and tell them what
you are going to try to achive. That way you will know which unit(s) to go with.
Just my opinion....I really don't think know if the Buttkickers are better as far
as vibration, or if they are worth the extra bucks.