The cable has a dual purpose. One end is used for charging the speaker, the other end is the line-out connection for your home theater receiver.
First cut the supplied USB cable connector off at about 3 inches from the back of the connector. Strip and tin the wire ends with solder. This needs to be done on the USB A and B connector sides. ON the A side, we don't need the Green and White wire as these now carry audio for the mini-B connector. Insulate the ends of these 2 wires so that they are electrically isolated from the cable. Make sure not to create a short circuit.
Cut the RCA connectors off one end of the cable. I normally cut so that I have enough cable left so that the connectors are usable on future projects. Strip and tin the wire and then connect the two grounds together and the 2 signal wires together. The output of the speaker is mono and the home theater receiver input is stereo so we feed the same signal into the left and right terminals of the home theater receiver.
Now solder everything as follows:
- USB White connects to RCA joined Red/White
- USB Green connects to RCA joined shield
- USB Black connects to the the USB cable "A" black (GND)
- USB Red connects to the USB cable "A" red (5V)
Before soldering, cut heatshrink as needed to insulate the connections after soldering. To give overall strength, a heatshrinked a couple of pieces over the entire connection area of the cable.