If you put the open dining area behind the loud and long echo is gonna be hella distracting. What you will never in your life do, but should if sound is all that matters, is put the system in the open space and the couch against the wall. Well, not right against. Out a little, wherever is the best balance.
The speakers will then be way out from any walls and throw a deep image like nobody’s business. The echo by the time it reaches you way back against the wall will be diffuse and create a sense of spaciousness. I actually set the system up like this one time at an audiophile club that met in a church basement. They never had the creativity to do anything like this. Everyone was amazed how the system they all thought wasn’t capable of imaging suddenly sounded deep and wide and holographic. Oh, I also used a tape measure so set it up in half the time they always took
Even though they all knew it sounded better than they ever heard they of course never set it up this way again. Because audiophiles love the talk, a whole lot more than they walk the walk. All hat and no cattle, as they say in Texas. You’ll never in a million years even try this idea just to see. But its totally the way to go. Bonus points: easy back of gear access, great excuse to educate guests about audio. If you did it. Which you won’t. Which I can understand. But you asked. So I answered.