It appears that the seawater kit inserts a 'T' connection after the fresh water intake solenoid. Must be a one way valve. The raw water is straight into the T.
A minimum pressure of 10psi, but no maximum discussed.
The remote pump psi is not mentioned. My wash down pump is 70 psi. Maybe too much, but I do have a fresh water pump which does not shut off, so switched it would work fine.
When I find a round TUIT I will give it a go