I was wondering whether it is possible to control the volume of the Music App in Windows 8 independently from system's sounds. It is quite annoying that the Charms Bar in the Music App controls the system's volume.
Most of the metro-style applications which play sounds implement the ISimpleAudioVolume interface. It is allowed to set a session-wise volume, but only if the developer had made use of it in that manner.
From the documentation:
Hence, unfortunately, unless the application itself has implemented session-wise controls, you are out of luck in this regard,