Hi Jim,
I know you are a "picture guy" more than a "sound guy"
, and I am quite the reverse (or propably was).
First of all your room looks fantastic (Chapeau!!). Can you tell me why you don't put your front wall as an option? Do you have a faux wall?
By the way bass is non-directional but either placement of the sub or yourself in the room will greatly affect how loud you hear it. Also, sometimes due to room modes you may have bass SPL varying a lot within few inches (no joke), so that you may hear it louder in an ear than the other and this gives an effect of being directional but that is not so frequent, so don't bother (I was just replying to your question).
You can use an amazing program if your room is a "shoe box" to similate how good your boxed sub(s) will do at your listening position.
http://www.pvconsultants.com/audio/r...s/room060d.exe
It will help you a lot. If you can't find a sweet spot for a box, only then you may propably consider an IB (but I am large box biased).
Regarding vibration of the projector, as far as it is mounted to a hard wall, I believe you will never have any problem. FYI, I have dual 18" in my 1800 Cu Ft room and no problem at 125 db+ ...nada!
Have Fun!