Hi, I have a Harmon Kardon AVR355 and have recently connected 2 new speakers to it as the previous speakers weren't good enough. I don't have a subwoofer or centre speaker yet, but have tried to set it up as i still have 4 good speakers but it always seems to think I have a subwoofer and whenever I play a song with a lot of bass the volume of the song seems to go down for a moment and the song seems to be fading in and out. I set it up, properly in the settings saying I had 4.0 but its not working, what have i done wrong?