I'm in the process of treating my listening room's acoustics. After doing some research, it looks like some are of the opinion that one must 'kill' the first reflections by placing sound absorbers right behind the speakers. Others prefer to put diffusers right behind them. Which approach is right? I'm definately going to put diffusers (3 Furutech panels) on the wall behind the listening couch, heavy curtains (velvet) on the side walls to cover up glass windows. I have relly high ceilings, about 15 feet. Any feedback will be appreciated.