This mainly concerns surround sound systems, with a subwoofer. It is possible to wire multiple speakers to one channel, most useful for subwoofers. Even though bass is nondirectional, the user can still sort of place it. I create "surround bass" with one subwoofer channel. Enough intro.
I purchased two old Sansui LM-110 multi-driver(woofer and tweeter with a passive crossover) and placed them around the back wall till i liked the positioning. I then replaced my ht-z320 subwoofer with a Samsung PS-WX50(from the HT-X50 system). The X50 went in front, under the TV. The wiring to he speakers must be exactly as follows, lest the amplifier in the main unit repeatedly shut the unit down to protect(PROT then shutdown) from damage.
This is easier to do if you know how to solder(it also grants better sound), but can be achieved with a twist on wire connector and wire strippers.
The purple plug positive(denoted as a + inside a circle) keeps its wire, going to front woofer(Samsung PS-WX50) RED. Cut some speaker wire to the back woofer last on the route the wire will take to the rear woofers. Split it, then cut one of the two wires on the speaker wire at the other woofer. strip both ends. Do this to two equal lengths of speaker wire. Split and strip the joined ends of the first wire and connec both ends to the black port on the front woofer, the othe ends to the back woofer RED ports. Take the other wire, join the unsplit ends to the negative wire(helps to cut that short) in the purple plug, using your wire nut. Strip and connect the other ends to the black ports on the back woofers. This basically is a series setup. The back woofers are one one parallel circuit, but are powered as one speaker. therefore, the front speaker and both back speakers(acting as one) are a series loop. To simplify, unit + to front red. Front black to both back red. Both back black to unit -.