Have you installed the Alpine HiFi amplifier yet? You'll want to take your initial electrical measurements at the branch-audio connector under the seat. The front channel outputs of the base audio system are supposed to be full-range and use the 4-pin connector at the 6.5" midbass enclosure to interface with the door speakers.
I believe the front channel speakers are wired in parallel with the underseat midbass drivers. I recall noting a cap integrated into the enclosure/connector that likely is intended for the woofer. I wish I could provide you pictures, but I sold my enclosures to Technic. He might be able to disclose where the cap connects at the 4-pin connector.
I'm most curious in your findings as I haven't yet graphed the electrical output of the base audio front channels and am really interested to see what sort of normalization the Alpine amp is responsible for with regard to installations that don't require coding.