Sound Loss

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. 

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.