THis is a advanced question, but here goes. I have a 998c SI from last year bought new, its on my boat on transom w the SI transducer. Works great just some things I noticed the other day. I got a new 958C HD DI for the bow in april. I run it thru the terrova80 using US2, I dont use DI w this unit. The 958 shows WAY better 2D sonar than the 998, its very sensitive even when turned down, I have the ducer option set to US2. I tried swapping the 998 to the bow for a bit, and set the unit to US2 as well to see the difference. Now the 998 still shows the same pictures, just not as detailed and strong. When I go over a bait ball its just that, a bunch of dots like a normal bait ball. When they come by the 958, I can see the bait ball and even see fish arches in/around the bait ball. Even if I turn up the 998 and adjust to the max I still dont get the detailed returns like the 958 up front. All software is up to date. Im thinkin I have marrower beams up front or higher frequency and thats why returns are better? Im very experienced w these units, Im in advanced mode and know how to adjust for surface clutter, sensitiviey, chart speed, etc. After doing some reading I see the 958c HD that has DI has a diff dualbeam frequency than usual, the refular dual beams are all 20/60 but the DI units are 200/455 w 16/25 beams. For testing purposes I turned on FishID and I am getting blue AND orange symbols, so the US2 is displaying 2 beams it seems, but minn kotas site says the US2 is capable of 20/60 only. Can anybody tell me what frequency I am seeing up front w this 958. 2D sonar is so good Im thinking of selling the 998c SI and getting an 1158c HD DI as I dont use sidescan as much as i thought. THanks in advance Im stumped on this one