I know this might not seem a huge upgrade to some, but for me it was. I upgraded from RP-500c center channel to RP-504cII. Front L/R I went from RP-500m to RP-600mII. Got it all setup, ran Audyssey, then manual distance, levels, and crossovers. I tested some scenes with surround and dialogue. I then played some music. I'm extremely satisfied with how it all sounds. Dialogue is crystal clear while there's a lot of sound effects going on. I streamed Chris Cornell from Audioslave singing Nothing compares to you unplugged and it sounded amazing. Next up, another sub and blu ray player.