Buttons VOLUME and MUTE work only on the signals decoded internally by the player as the MP3 or when the sound is stereo downmixed if you choosed LPCM 2.0 for example. For all other home cinema audio stream, sound is outputed in bitstream, it means it is not decoded by the media player. You can operate the volume only on an audio stream already encoded. Then, for audio stream in bitstream mode, you will have to use VOLUME and MUTE buttons of your home cinema amp remote control. If you want, you can save the control volume buttons on the Zappiti remote control with the programmation buttons (see user guide).