I'm with Trevor on this one. Your layout is a fuc&*$# disaster and you shouldn't spend any more time and money on it.
I'll go a step further and say you shouldn't have any speakers given the restrictions. How do you expect to enjoy the stereo effect?
Given however that I am an optimist and keen problem solver, here's something to consider. How about you keep what you have and add a sub like Trevor suggested? Then, when you need to enjoy a real soundstage, how about temporarily moving the speakers a couple of feet into the room and placing a chair at position (16,9)?
For all other times, you can listen to a piss poor distorted soundstage with no imaging so you can really appreciate those (16,9) moments. Kinda like when I rarely drink a gin and tonic to remind myself how much better life is when I'm not drinking that awful poison.
