Front or Back wall diffusers

You have a very nice system.  If you diffuse the front wall between the speakers they will image even better which is really saying something.  The idea of diffusion is to scatter the signal so the reflected sound doesn't return to the listener as a single competing signal.  You don't want a second signal competing with the direct signal from the mains.  As a rule of thumb one cannot over diffuse a room so you can be aggressive with the amount of area the diffuser covers on the front wall.  If you diffuse the front wall and use bass traps in the corners the DAWs will really sing.  Good luck and Cheers