Both the E5ti and E55tis are some of the easiest loudspeaker loads to drive. The impedance in bass frequencies is above 8 ohms which makes even modest power receivers have no issues driving the speakers. I do recommend using a powered sub for both music and movies to compliment the bass extension. They don't have as much deep bass as their physical appearance (E55s) would suggest, but they do play extremely loud and clean without bottoming out.