Since you have a difficult WAF restricted room, the only thing that could produce significant movement of the needle sonically would be a consultation with a professional acoustician like PoesAcoustics (Matt Poes) or Anthony Grimani (Grimani systems) who have a knack for measurements and discrete non-invasive treatments (made to look like a regular wall/ceiling, room decor, etc), probably a discrete in-wall sub, tuned resonator at a feasible spot, etc.
(Beyond the scope of a forum thread).
Actually...talk to Anthony on this one, if you can catch him (if he ain’t too busy).