For me, I feel that "synergy" happens when the music flows effortlessly and just feels "right". This can be for a number of reasons and may only happen when you change only ONE component, All of a sudden there it is.....Click.

I have been playing with some very basic room treatments recently. Very basic in that they are unwanted album covers that I have placed to deal with wall reflections (If you take a double album cover and make a sort of tent shape out of it and then attach it to the wall). In addition I placed a half open double cover on the top of each speaker. I suspect that it is interfering with reflections from the rear wall and maybe ceiling, but what I do know is that everything seems more right.....explain that? Oh yeah if you invert the covers on the speakers it sounds different again.