I would start out with obviously the Tri Traps. Side wall reflections are somewhat personal preference. You can either use absorption or diffusion for the reflections. I've even had folks effectively use both (absorb the far wall reflection, diffuse the near wall reflection). Behind the speakers in the center, personally, I prefer absorption there but again, that's a lot of preference.
Some additional bass control benefit could be had by using some of the Monsters on their sides on the floor leaned against the wall behind/between the speakers.
I would start with some combination of the above and see how it goes before committing to where to do the rest of if something else needs to be added.
Bryan
