Sound Loss

During playback of music or while in 3.1 set up, my Marantz NR1609 seems to lose power. My speakers are B&W CWM664 for right and left and use a CWM362 for a center channel. Not sure why, but can anyone help me troubleshoot this? Thanks in advance.
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. 
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I'm wondering if you are trying to use some surround mode, like Dolby Pro Logic, when you play 2-channel music.  Dolby Pro Logic has unpredictable results on 2-channel audio that has not been specifically encoded for Dolby Surround.  It is very common to have instruments fade in and out during the song when using one of these DSP surround modes. 
Ahhhh yes, using a DSP mode instead a 2-channel stereo mode for music.  Thanks guys. Such an easy fix I couldn’t even see it.