I have a Volvo S40 2.4i, I'm interested in upgrading the car audio. where can i
get/view a wiring diagram and current audio/power specifications for the
factory OEM amplifier that is in the trunk that powers the door speakers?? And
as i understand the OEM amplifier is wired much different-(more wires) than the traditional wires-(power,ground, remote, and speaker wires) that complete any aftermarket amplifier... Is it possible for me to maybe buy a more powerful amp through volvo or someone else which input and output connections are configured for my current OEM wiring harness?

to make all of the above more short and simple -

*how powerful is my OEM amplifier-(total wattage and per channel)
*is this amplifier replacable with a more powerful one?
*where can i view a wiring diagram for the amplifier/car audio?
*what size and specs-(power rating) are my door speakers?