Players' buttons have a double function (not all for the moment) when you push and turn them.
in the manual :
RIG VOLUME Knob (9)
The RIG VOLUME knob controls the individual volume of the current Rig, like a channel volume. Unlike MASTER VOLUME, this setting will be stored as part of the Rig. For a detailed description please refer to Rig Volume chapter.
Push-dial this knob to control the Bluetooth® volume as well as the volume of your USB playback (“DAW Volume”)
Thanks! I read the manual but somehow missed this.