You can link your HDS7 and 7 HDI if it has a Ethernet cable. I mounted my LSS unit in the storage compartment in the front of my boat. My HDS 7 sits at the helm. I then have an Ethernet cable ran from the LSS unit to the front mounted fish finder. I can operate both units independently or together. It is awesome.

SS lets you get quietly into an area and not spook the fish. You can also draw a line to structure, it tells you how far it is, and.... to help you from guessing, you can set a waypoint directly over that spot. Great for edges of weedbeds or anything else you can think of. Heart starts racing when you see something on the bottom for the first time (like an old tire)