Was the guy you bought them from even the original owner? How could you not know what speakers you have especially if only about 3 years old.
The trim control adjusts the frequency response of the sub kind of like using EQ but with preset settings. Flat is a flat FR, where Half and Full are designed to help compensate for subwoofers in general having FR issues in small rooms. Load is supposed to be for firmware updates though I’ve never seen one yet.
I’ve used the Half and Full settings to boost the FR at around the 40Hz range in two rooms where I had large dips due to room modes.
