Aside from screen permeability to pass sound, you also give rise to odd reflections etc.
Only solution I can see is the one I've used - a screen that retracts when you want to listen to two channel (and in my case a different preamp/amp that sounds better but has lower output than my AV amp path).
My main speakers around now outside the screen area in my new listening/viewing room, but in my old smaller room, the speakers were right behind the screen - minimal loss of SPL if you get a quality screen made for audio transparency.
