Humminbird issues - help needed

I have always ran Lowrance until this year. I have heard good things about Humminbird so I was excited to give them a try. However, I am having some issues with them and wondering if anyone can help me out. I have a 998c SI and a 958c SI at the helm of my boat. They are connected with an Ethernet cable and I updated to the latest software this past week. I typically fish in less than 40 feet of water. I would like to run the 998 split screen with map and side scan and then run the 958 with traditional sonar and down scan. When I try to run them like this the 958 gets a lot of interference and the depth bounces around a lot and causes the screen to shrink (see the attached pictures). I am not sure if the transducers are too close together but when I just run 1 unit they work fine. I have contacted Humminbird and they pretty much said that was normal and there was nothing that could be done which surprised me. Does anyone else have a similar set up and has a fix for the the issue I am referring too?

Thanks. I will try that.

This site has answers for Humminbird problems.http://forums.sideimagingsoft.com/