The crossover upgrade involves air core coils, which are larger than the stock units, and require mounting them adjacent to the stock crossover.
The response graph is an average of the left and right speakers in my listening room, with the UMIK-1 calibrated mic, 1 meter away from the speakers, on the listening axis. It is gated to about 50ms. Measuring bass in a room is always problematic, so don’t worry about the graph below about 250Hz.