Fathom X + Fathom S

Hey, i am planing to use bluerobotics Fathom X, Rpi and Pixhawk to control my ROV. But when i was going through your website i found that Fathom S could be stacked above Fathom X and the benefits of both the boards could be used.

I would like to know what additional capabilities will my ROV have if i add Fathom S my already existing Fathom X, Rpi and pixhawk boards.

PS : I am a mechanical engineering student and have very limited knowledge on Serial communications and Ethernet.

*add Fathom s TO my already existing

sorry, missed the TO in my question.

If you already have the Fathom-X+RPi+Pixhawk, then about the only thing a Fathom-S interface board set would give you is the ability to add an analog camera.