I went down to my studio and set up the two cabinets together with the MV-50 AC and played a few numbers with the BTs, disconnecting one speaker a listening to the difference it made as I did so, switching the impedance switch to match the speakers and yes there is a difference. It's not massively apparent at first because it sounds good anyway, but with the second speaker connected, as you crank up the volume it is clearer and bigger as one would expect.
That said, most guys who play at home would be delighted with the sound a single BC108 provides and I doubt anyone in the house would encourage the player to buy a second one to use in the house.