Each of the 16 Performance channels has its own volume control.
If you have a PC and a midi interface, the SoundDiver (not to be confused with a sound driver) librarian software (that comes with the JV-1010) will allow you to modify the 32 User bank Performance setups.
NOTE: I've had problems and error messages when I start up SoundDiver with the JV-1010 on. IMHO, the instructions for both the JV-1010 and the SoundDiver software could be improved on. If patience and trial & error prevail, you'll find a cool set of sound possibilities with the JV-1010.
Good luck.