I came across a similar issue when playing video files through HDMI. I had to turn the sound up on my receiver much higher than normal (as compared to listening to cable, DVD, etc). What I did was turn the volume up on the DSM-520 unit itself using the remote control - it was only at 50%. Can't say that this is the same issue when using RCA or other inputs besides HDMI on the DSM-520, but you might want to give it a try to see if it helps.