A and B terminals are intended for wiring 2 sets of speakers in 2 different rooms. The idea is you can have either set of speakers playing, or both at the same time, as long as you don't turn it up too loud.
This type of amp only has one stereo amplifier, the A & B switch is just that, a switch. You can use it for bi-wiring, but it can't bi-amp, because there's only one amp.
Bi-wiring is connecting the drive units individually, using separate wire, back to a common amplifier.
Bi-amping is connecting the drive units individually, using separate wire, back to an amplifier for each drive unit.
Bi-wiring is of questionable benefit.
Bi-amping really works.
