The speaker placement you mention is a non-starter for our situation. Trust me on this - we have a surround system upstairs and my wife never turns it on. She just listens to the TV speakers. Also, it looks like the corner horns wont work because they have an open back that would be closed off in the bookshelf cabinetry.
The basic plan A is to throw some Paradigm Atoms into the bookshelves and put an MTM center channel into the mantel.
Plan B is to put 3 pi towers in the corners, no center channel, inwall surrounds, and a subwoofer on the back wall. I know that I am reducing the performance of the system. But would this not sound far better than plan A?
This picture shows how I would try to build 3 pi towers.