Grasshopper
You and the wife might want to take a look at the two different types of freestanding absorber/diffusion panels below as they come in many different styles and colors. I am using 2' x 4' freestanding panels in two different rooms directly behind the speakers. If she will not allow them to stay in place all the time they are lightweight and easy to move so they can be put in place just when you are listening in the sweet spot. You might be able however to find a color and design that over time will just blend in.
https://www.gikacoustics.com/product...usor-absorber/
https://www.gikacoustics.com/product...usor-absorber/