Another 'vote' to keeping the amp you have now and letting the AVR drive the remaining speakers since you said movies are 'secondary'.
A good quality AVR will have plenty of oomph to drive a center and surrounds. And you can keep the Muse for the sound you cherish now for music.
A good quality AVR will have plenty of oomph to drive a center and surrounds. And you can keep the Muse for the sound you cherish now for music.