From a music source, ie a laptops headphone output socket, the small signal output can be amplified and connected to the audio amp on LedLabs and then fed to the 8 ohm speaker, one way to do this is to use a 3.55mm stereo cable which plugs in to the laptops headphone or speaker output port. The other end can be cut to expose the wires, there should be three wires, left and right audio, and a common ground, this is why when looking at the stereo jack cable plug, three separate bits of metal is seen separated by a usually a black insulator which represents left and right audio and the common ground. some newer cables have four separations on the plug and this is usually a video connection, however it is not a standard audio 3.55mm.
When the wires are cut, wires can be soldered to these ends to suit LedLabs connectors, the ground wire can be connected to any 0v on LedLabs, and one of the audio wires can connect to the LM383 audio input, then the audio out to the speaker, the volume control should be set quite low on LedLabs just to cut out any distortion on the speaker.
The other audio wire can be connected to a bass boost circuit and to the LM3914 to show a vu meter response. See vu project circuit diagram below. It uses an LM314 op-amp and is quite simple to build using the bread board.