Sound Loss

Do you mean you just lose sound or does the whole unit lose power and go dark?

During music playback, when the singing starts the music seems like it goes to the background. During a movie, the background seems to be set further back when there is voice. 

Do you have the center channel volume level set correctly relative to L/R?  Also, check sound settings menu to see if you have some funky sound processing enabled.  How does it sound in 2-channel/stereo mode?  If that sounds ok it’s probably a setting somewhere.  Hope this helps.