Just took a quick look at my SH 1700 (same radio, but with built in GPS) box, where it says:
"The GPS Position of a received DSC Distress or Position Request call can be shown on a compatible GPS Chart plotter simply by connecting 2 NMEA wires. "
Technically, I think they mean 4 wires (2 additional needed beyond the 2 that allow the radio to recieve GPS data so it can transmit your own DSC call). NMEA 0183 can both send and receive data from other devices. The original AIS radio's were Standard Horizon's and Icom, and both only do 0183.
Don't have my manual handy, but it should tell you how to hook things up. If you have any issues, call Standard Horizon, they have great customer support.
When someone makes a DSC call, you will hear an ear splitting screech from the radio which tells you such a call has been made. I only saw it once on my old boat (SH 1600 radio as well), and it switched my radio to channel 16, and displayed the GPS coordinates of the boat making the call on the screen of the radio. I did not look for it on the plotter, as the guy quickly came on the radio to apologize to the Coast Guard because his kid had been playing with his radio.