Jigging15 and Daddy Rat both gave lots of good info. Last year I was in your same boat as you trying to decide what to get. I ended up getting the HDS 7 bundled with the LSS2. I have it setup like Daddy Rat with the SS, DS, and 2d in the back and then added another 2d transducer for the trolling motor. It’s a pain sometimes but I move my unit back and forth. I ran another cable from the LSS2 to the front so I can see the SS and DS in the front also. It's nice to be able to see the SS and DS in the front. The SS and DS don't work very well if you are not moving much, so it’s not as useful in the front.
I have had my unit for about 10 months now and can't imagine fishing Truman without it. I can scan an area that I want to fish and tell within minutes if it’s holding fish. It takes a while to get used to it and figure out what you are looking at and I'm still learning every time I go out. If you’re like me and don't get out all that much, it’s hard to spend time on the water looking for fish and not fishing, but it can pay off if you look. It’s harder in the spring to decide on a location to fish when the fish are scattered and you’re seeing a few fish everywhere. This winter, it has been easier to find concentrations of fish but getting them to bite is another thing. As the other guys have said screen size is everything. The 7 works but it sure would be nice to have a larger screen!