I got the kit yesterday. I did more measurements. The previous data of the HeadUnit was done with a source that is flat from 200 Hz to 20 KHz (test take 3 second). For my new measurements, in order to get the response at lower frequency I changed the source to 20 Hz to 20 KHz (test take 30 second).
Here is the response of the amplifier for switch position #1 and #2. As you can see, there is a crossover in the amplifier. Frequencies below 120 Hz are sent to the woofer under the seat. Frequencies above 120 Hz are sent to the door midbass and tweeter. The purpose of the switch on the amplifier is to attenunate the woofer output, 0 dB in position 1 and -4 dB in position 2. My take is that if you have a 4 Ohms woofer then position 1, for a 2 Ohms woofer then position 2. This is to normalize the response of the woofer with the midbass and tweeter.
I did an estimate of the composite response of the HeadUnit and the Alpine amplifier. The HU is set for Bass=0 and Treble=-5. This appears to be the setting that gives me the best flat electrical response. I have not measured the acoustical performance yet.
Note: The passive crossover that will fit in the door has a lowpass for the midbass driver and a highpass with attenuation for the tweeter. I have not measured it yet.