Hi Martin,
Could you try somethings for me please?
1) Check that you do not have the Graphic equaliser turned on (you may not have even loaded it - if so go to 2). If it is turn it off (does that cure the problem?) if not then :-
2) Plug a set of headphones into the line out socket at the back of the B2 and confirm that when listening through these the volume in each ear is the same.
3) If the volume on the headset is the same in each ear, and assuming the plugs to the speakers are not shorting, could you swap the Speaker plugs over and see if the quiet speaker swaps with the plugs or remains on the same plug pair.
Thanks, Fred.