I asked the same to the MGM team and the answered:

In current Car/Boat versions are no possible set "cut-off voltage", here is fixed value ca 0.85V/cell (Nixx) --> it is ca 2.2V/cell A123.
Nixx batteries have only automatic number of cells setting (this value is no critical for Nixx) - this is applies for all controllers, no only for car/boat. When you will start with charging A123 cells, cut-off value for A123 will be correct.

I undestand that programming for nixx cells will work for a 2.2V cutoff using any number of A123 cells.