Well I just looked at the Humminbird manual for the 997. Looks like you don't have MAX mode on the 997... but you do have a sensitivity for the 2D. While you have 2D active on your screen hit menu once and the X-press menu will pop up. Look for Sensitivity and change it there. You have a regular "Sensitivity" and a "SI Sensitivity".

See page 69 and 85 for the 2D sensitivity. You can change in X-press menu or your Sonar tab under regular menu.
http://store.humminbird.com/media/do...531559-1_F.pdf

On the 898, 998, and 1198 series.... you can change sensitivity for the 2D, DI, SI and also the individual 83 khz beam for 2D. You should be able to change the DI sensitivity on your unit also but it looks like it is doing fine. As long as you can see the fish in all 3 screens your are good to go. If they are showing on DI and SI and not 2D then that sensitivity needs to go up till they do show up. I use the 2D alot to help determine a depth range. It is helpful.