The simple answer to this question is higher output power (more Watts) and reduced current draw (play your music for longer periods). To give you a comparison between Class AB and D class, the normal output of a standard Head Unit ( class AB) is say 40-50 watts Peak per channel. The Fusion 600 Series Head Units (MS-CD/IP/AV600 D Class) have a rating of 70 Watts per channel and due to their efficiency consume less power per Watt of output. In essence you can go louder for longer. The other major benefit is that the D Class amp in the 500 and 600 series is that it's 2 Ohm stable (stereo).What this means is that you can conect 2 x 4 Ohm speakers per channel in parallel wiring configuration. This produces more power but is divided between the 2 speakers. Eg. at 4 Ohms per channel ouput is 26 watts RMS and at 2 Ohms it is 43 watts RMS, so divided by two is 21.5 watts RMS per speaker.
The theoretical efficiency of class AB is about 75% as well with a real efficiency between 50%-70%; the theoretical efficiency of class D is about 100% with a real efficiency of more than 85%.The Fusion D Class Marine Zone amp MS-AM702 is a perfect example of a compact high output solution for the boating enthusiast that loves their music. loud