Merging two channel outputs together isn't a common practice.
Merging two home theater channels together then splitting the connection out to two different speakers isn't a common practice, because it tends to muddle the sound and create instability in your wiring, which leads to small electrical surges that can damage your equipment. However, it's a relatively simple process.
Instructions
1. Connect a speaker wire to the left front channel output of your home theater system then to the left rear channel output.
2. Intertwine the red connection from your left front channel and with the red connection from your left rear channel. Repeat for the black connection.
3. Intertwine the ends of another speaker wire into the two intertwined ends you just created. Twist the three ends together as tightly as possible, making sure all the fibers of the wires are twisted tight.
4. Hold the end of the solder over the exposed ends of the wires, and drip over the connections until covered.
5. Allow the connections to dry and cool, then wrap them with electrical tape until completely covered.
6. Connect the loose ends of the single speaker wire you connected with the solder to the "Input" side of the speaker selector. Connect your left front and left rear speakers to the "Output" sides of the speaker selector.
7. Turn on your speaker selector, ensuring that both speakers are in the "On" position.
Tags: left front, left rear, speaker selector, speaker wire, your left