The 788 HD DI. Is a new model that only has DI. Smuckey is correct that with the 798, 800 and up series that had SI, Hummingbird came out with a download to give you DI after Lowrance came out with DI. It was a competitive offering by Hummingbird. You will not be able to get SI on the 788 DI.

While DI is cool, in my opinion the SI is awesome. I would spend the extra to get it. I cannot tell you how many honey holes i have found 100'-150' off the side of my boat that I would of missed because I would never have gone over that spot.