We spent a small fortune narrowing the width of our room by a few inches so that we could build a false wall to soundproof the party wall. We have SbX boards which are filled with a honeycomb membrane of sand mounted on some metal studs which are isolated from the party wall with sound insulation mineral wool fills the voids. On top of the Sbx is soundproof plasterboard, two layers with the joints staggered. It's a very effective setup. I am now thinking that it might make sense to put a tv bracket on that wall, but I don't want to compromise the sound proofing by drilling into the wall for the fixings. Some people have suggested green glue can help seal the fixing points, but I'm not sure how that work.
There is an alternative which is for the TV to just sit on a cupboard (which is going under the TV location anyway, but if I do that i need to somehow find a way of elevating the TV stand (which has a rather large oval shaped base) by 12cm to make space for the soundbar to sit underneath it.