After upgrading to 9.0.3 - 1759466965 the setting for "Don't stop the music" can not be set on additional players.
I have players SB1, SB2, SB3 and SB4. If I navigate to Settings/Player the first player SB1 is selected by default and I can then choose the option for "Don't Stop the Music" and I can set the value to "Music IP Mix" or any other value. If I then switch to one of the other players, I can set values for "General", "Audio", "MusicIP" etc. If, however, I choose "Don't stop the Music" the player switches to SB1.