I'm a big fan of diffusion if you think you have a problem. Too much absorption results in a very dead sound. But if it's working as is, I'd leave well enough alone.
You could try moving your speakers and possibly your seating a little further back. I've got mine with the front baffles about 7' from the front wall.
These days, I spend most of my time listening at my desk which is set up directly against the back wall, so my seating is about two feet from the back wall. With my room, that puts me about 18ft from the speakers. At my desk, the imaging isn't as good as at my primary seating position, but it still sounds incredibly good.