Just to totally 180 your train of thought.

Can the screen pull down in front of your balcony window? Fixed frame is a bad idea personally. It will dominate your small space when you arent using it. This is not a dedicated space. It will look extremely "bachelor" in there otherwise. laugh

The mains will flank the screen and you have 2 juicy walls for surrounds. The center channel will have to be mounted above the pulldown frame aiming at the listening position. When not watching a movie you are listening to tunes gazing out your balcony. Could be cool.