The term 'SOUND-SYSTEM PART' can be broken down into two parts: the first PART, 'SOUND-SYSTEM', refers to a SYSTEM of electronic equipment used to amplify SOUND, while the second PART, 'PART', refers to a component of the SYSTEM. The crossword solution for this term is 'AMP', which stands for 'AMPLIFIER'. An AMPLIFIER is an electronic device that increases the strength of a signal, such as an audio signal, before it is sent to a speaker. It is a key component of a SOUND SYSTEM, as it is responsible for amplifying the SOUND so that it can be heard clearly.