It looks like you are planning to put all 4 speakers on the back wall from the CAD drawing. That is not really how 7.1 is designed to work.
I would recommend pulling the couch towards the TV a few feet, then placing the 2 back surrounds about 3 feet from the corners on the back wall, then put the side surrounds on either side of the couch. It looks like the best place to put the side surrounds is as far forward as you can considering the small wall you have to the right, and far enough foreward to be *above* (according to the drawing) the window.
That would be a great setup.
