I’m also building a screen to mount on the wall. I plan to rip some 2X4’s in half and screw them to the wall the size of my screen. Paint them all black, then rap the material over the 2X2’s. Trim the edges with some MDF and paint them to match. You could do the same, but just don’t rip the 2X4’s down. Space the studs so the speakers are in between them. You can build the frame and mount it with some angle brackets that you can find at any hardware store. Just mount them on the inside of the studs. Then trim it out.....