This does not address your question directly but may be of interest to this community. (FWIW)
Originally, Amel was reluctant to offer the 160 Lt/h, firstly because it was so expensive but also because their experience over 16 years with the Super Maramu had shown the advantages of the 100 Lt/h duo system (220v & 24v) that can run on Volvo alone as well as Onan.
If you are the only one to face this issue, then the previous comments are pertinent to finding a solution.
However, if other 54 with the same setup as yours, have experienced comparable problems, then it may be a design issue: To the best of my knowledge all 54 have the same "Xmas tree" (the horizontal pipe that distribute sea water to all consuming units (A/C, Anchor wash,...), except volvo & onan that have a direct connection to the water chest.
That pipe may not be big enough for your setup but it easy to change.