I took another look at your photos and if there are windows on the left side you could add some nice thick drapes and achieve generally the same absorption as using some commercial absorption products. If it is appropriate to add drapes you could balance absorption by hanging a sound absorbing decoration above the couch on the right side.

My room is open towards the back too and it looks like there are stairs towards the back of your living room. That might not be all bad. Typically you would use sound diffusers versus absorbers in the back of the room to improve the surround effect.

One more thing is that you could be getting a center speaker reflection from your coffee table. Do you have any trouble understanding dialog? If so, try moving the coffee table out of the room and see if things improve.

Just my .02 cents.