RBeav is right: the 597ci HD DI unit is an awesome unit but cannot be linked to another unit. You would have to go with the 788ci HD DI unit if you want to link a smaller DI unit to another.

With our Side Imaging units you get both Side Imaging and Down Imaging sonar, but since the Di sonar is derived from the two Si beams; it is not as clear as a DI unit would be.

For the $2,000 price range you are looking at the 798ci HD Si and 788ci HD DI units. Be sure to buy the Ethernet connection cables for these:
two of the AS-EC-QDE adapter cables and
one of the AS-ECxxE cables (replace the “xx” with the cable length that you need): http://store.humminbird.com/category...thernet_Cables

The units will be able to share GPS Receiver data, waypoints and water temperature (no sonar sharing between a DI and non-DI sonar units).

If you wanted an Si unit at both ends of the boat you could go with two of the 798ci HD Si units and share full sonar between them. That would probably put you a little over the $2,000 mark though. I would contact the board sponsors and see if they will cut you a good deal on buying multiple units and cables.