When playing your mp3 music collection from the PS3 connected by HDMI, there is no sound heard in the rears speakers of your surround system. Instead the output sound is 2.0 (stereo Left&Right only), making music not feel "alive". There are two ways you can solve this little issue. One of the easiest way is to go into the PS3 Settings/Audio Output Settings/HDMI and disable (uncheck) everything in the list including all Linear PCM. Save and then play the mp3. Now you'll hear music in surround sound. But when playing a PS3 game or movie, put the settings back to the way it was, typically check all boxes.

Another way is to use Optical cable for the sound output from PS3 to the receiver. Make sure you select Digital Out (Optical) in Settings/Audio Output Settings. Also change your receiver's setting for Optical input.

I find it inconvenient having to change the setting each time I want to listen to music, but this is just how the PS3 plays mp3 through HDMI.