I recently upgraded my CD source(Electrocompaniet) and preamp(Pass Labs X1). My Nautilus speakers sound profoundly more involving and interesting. I keep sneaking in for another listen late at night. This is not just a new sound, it is sweet and compelling music - system almost disappears.
I am quite certain that a change in speakers would NOT have produced what I am currently hearing from my system.
BTW, on the question of speaker upgrade, I have come to the same conclusion that Psjulian has ... Revel.