Hi Stevew...,
The amplifiers in the B2 are a 'bridged' design which means there is an amplifier connected to the red and the black output terminals. The amplifiers work in push-pull to increase the output power. The diagram shows one channel -
The problem with many speaker switch boxes is they connect the black terminals, assuming them to be common to both channels, and only switch the red terminals. This type of switch box cannot be used with the B2.
There are some that switch both terminals and also allow for both sets of speakers to be used at the same time - Monocor SPS20S for example.
Paul
Brennan Support.