To connect a Brennan JB7 to an external amplifier, first, locate the audio output jacks on the back of the JB7, which typically include RCA outputs (red and white connectors). Use a pair of RCA cables to connect these outputs to the corresponding inputs on your external amplifier. Ensure the amplifier is powered on and set to the correct input source to hear audio from the JB7. Finally, adjust the volume levels on both the JB7 and the amplifier for optimal sound.