If it were me, I would find a way to convince my wife that actually adding a wall (maybe with french doors in the middle) was the answer. My room was 14' x 26' and I added a wall to make my audio room 14' x 20'. That left my wife a 14' x 6' foyer to decorate. You could put your wall in so that your audio room was 16' x 22' (minimum) and that would leave a decent dining area.
Before I changed my room, I experimented with my system by swapping the speakers back and forth from the long wall to the short wall. I preferred the short wall. With the speakers on the long wall, the only advantage was that your side walls are a great distance from the speakers. This basically takes away the "first reflection point" problem. This type of setup gives really great horizontal (left to right) imaging and separation. But, because you can't pull the speakers off the back wall much without them being right in your face, your image lacks depth, its not very three dimensional.
When I placed my speakers on the short wall and pulled them out about 6 feet from the rear wall, the music was much more 3D. (http://www.cardas.com/insights/index.html)
Before I changed my room, I experimented with my system by swapping the speakers back and forth from the long wall to the short wall. I preferred the short wall. With the speakers on the long wall, the only advantage was that your side walls are a great distance from the speakers. This basically takes away the "first reflection point" problem. This type of setup gives really great horizontal (left to right) imaging and separation. But, because you can't pull the speakers off the back wall much without them being right in your face, your image lacks depth, its not very three dimensional.
When I placed my speakers on the short wall and pulled them out about 6 feet from the rear wall, the music was much more 3D. (http://www.cardas.com/insights/index.html)