You really need to think this out before you do anything. You can never exceed the 2amp that each FI5002 is rated for. If you plan to have items into each box (say 1.5 amps into box one and 1.5 amps into box two) together with all bus wires connected, you have 3 amp regardless and exceed what the rating of the box(s). The way you can work around it would be to take the NMEA2000 cable that runs between the two boxes and only connect the data wires (White and Blue) and leave the power wires disconnected (Red and Black). Now the boxes will be on the same data bus, but isolated from each other for power. Then you could power each box separately and the power draw will be of only the items plugged into each box. The data wires will allow the entire bus to communicate properly.