Here you have save/load tutorial which plays both sound and music based on value of variables
Which are controlled by sliders
Maybe it will also fix your JFXR issue
Basically you use play sound on channel to play music
And play sound to play sounds
Where you can have different variables for different sounds
For example for game sounds you could have Save.Settings.GameSound
And for UI sounds Save.Settings.UISound
And now you would have 2 separate vars to control volume of each