A Marine Zone Amplifier (MS-AM702) is needed if;
1) you are planning a multi-zoned marine audio system, comprising of three or four zones
2) you are planning an audio system that has more than four pairs of speakers
1 zone system 1-4 pairs of speakers no Zone Amplifier needed
1 zone system more than 4 pairs of speakers Zone Amplifier needed
2 zone system 1-4 pairs of speakers no Zone Amplifier needed
2 zone system more than 4 pairs of speakers Zone Amplifier needed
3 zone system Zone Amplifier needed
4 zone system Zone Amplifier needed