Ah, I thought you’d never ask. Those dual terminals are separate connections for the driver (woofer) and tweeter (in a two-way speaker) to allow for bi-wiring or bi-amping your speakers. Let’s look at what those are and how to do them.
In bi-wiring, one cable pair delivers high frequency information to the tweeter and a separate wire pair delivers low frequency signal to the driver from the same amplifier. According to one theory, by providing each half of the signal a separate wire path, interference effects within the wire are reduced, producing better sound. We're not in a position to explain in-depth, or for that matter prove or disprove this or any other theory. What we can do is tell you that in many systems, bi-wiring does indeed make an audible and worthwhile difference. The better the speakers and electronics you have and the more discerning a listener you are, the more likely bi-wiring will make a difference you will appreciate. I was shocked by the difference bi-wiring made with LSiM9s in my listening room. The midrange opened up, becoming clearer and more detailed with improved three-dimensional imaging. Voices and other midrange sounds were more out of the box than with the single wire hookup. To bi-wire you need four lengths of speaker wire. For convenience and economy, most cable manufacturers offer bi-wire cable wherein two sets of cable are combined into one jacket. If you want to use the speaker cables you have now, just add a second set of the same cable. Be sure to remove the flat metal jumper cable between the terminal sets. Most receiver and amplifier speaker terminals allow you to connect two sets of wires. If that isn’t possible with your equipment, you can use the "A" and "B" terminals and set the receiver’s output to "A+B." It is all the same electrically but it is better to leave the "B" set of terminals free for connecting remote speakers. If you have lots of time on your hands and love to experiment, try mixing different types of wire for high and low frequency duties. Always use heavy gauge cable for the low frequency path. Try smaller gauge esoteric cable for the high frequency path. With a little experimentation you’ll find a combination of wires that works best for your system.
True bi-amplifying involves using an outboard electronic crossover, multiple amplifiers, and removal of the internal passive crossover of the speaker. We’re not going to tell you how to do all that because it is expensive, entails a lot of work and unless you REALLY know what you’re doing, you may get worse sound than you started with. Most folks drop the idea right about now in the explanation process. But a few brave souls try half baked bi-amping where two stereo amplifiers are used to drive one pair of speakers: one amp drives the low frequency section of the speaker and another drives the high frequency section and the passive crossover remains intact. The benefits of bi-amping compared to bi-wiring are subtle, but like choosing wires you can try different combinations of amplifiers to tailor the sound. For example, many audiophiles prefer the smoothness and silkiness of tube amplifiers for high frequencies but feel that solid state amps do a better job on delivering high current punch for woofers. By bi-amping you can get the best of both worlds. But if the gains of the two amplifiers are very different from one another, the tweeter will play at a level very different from that of the woofer and you will wind up with sound that is obviously inferior to single amplification. If you’re going to try bi-amplifying, use power amplifiers with identical gain settings or variable gain controls. Bi-amplifying is not for the faint of heart or the casual audio enthusiast.
Most important of all: REMOVE THE FLAT METAL JUMPERS BETWEEN THE TWO SETS OF SPEAKER TERMINALS OR YOU WILL DAMAGE YOUR AMPLIFIERS!