6 1/2" components in front doors
5 1/4" coax in rear doors
6x9 woofers in rear shelf
All crossover duties are built into the Monsoon amp located agains the back of the rear seat towards the driver'* side. Speakers are 2 ohm. Have not come across published power of the system. Head unit and amplifier talk through a data bus. Head unit appears to have a fixed volume output. Changing volume actually sends a command to the amplifier to adjust gain, similar to newer premium systems found in some Cadillacs. Cannot replace head unit without bypassing amplifier as of yet (have been told a databus/onstar/premium sound interface piece is in the works but last I checked was not released)
Realistically, due to the combination of 2 ohm drivers and crossovers built into amp this is a car where normally I'd either leave it alone and add a subwoofer or go big and replace the entire audio system.
Parts I've used in my own car to replace the OEM Monsoon equipment...
-Axxess GMOS-05 radio databus/onstar integration piece (used an extra 3.5" speaker mounted under passenger side dash for onstar/chimes, could be ran through door speaker similar to OEM setup if chosen)
-PAC SWi-ALP steering wheel interface for Alpine Head Units (various brand interfaces also available)
-GM double DIN dashkit, I used a Scosche kit because I prefered the rounded edges
-VW antenna adapater - Metra part 40-VW10
-Monsoon amplifier bypass harness - Metra part 70-2056
-Speaker harnesses - Metra part 70-4568 (4 pair for entire car)