You can use another audio device, such as a portable digital music player, with your system. This requires using a stereo audio cable with a 1/8-inch (3.5 mm) mini plug (not provided) that is appropriate for the connected audio device that plugs into the AUDIO INPUT connector on the back of the SoundDock system.
Adding another music source
Insert the audio cable from your audio device into the AUDIO INPUT jack on the back of the SoundDock system. If your iPod® or iPhone® is not docked, the connected device will play automatically once it sends an audio signal to the SoundDock system
Set the connected device to full volume, and then use the SoundDock system volume buttons to adjust the level
on the sounddock remote press and hold play/pause for three to five seconds to enable the connected device to play through the system if your ipod or iphone is charging in the dock
The iPod or iPhone charges while you are playing audio from the connected device
on the remote, press and release play/pause to switch from the connected device to your docked ipod or iphone