I have a base 9-3 with Dash and rear deck speakers...
All four are fairly useless so i thought i would replace and see if there was any difference. It seems the dash is 8 ohm and the deck are 4 ohm....

Do the doors come pre-wired from the factory or will i need to pull wire?
If not pre-wired does anyone have a schematic for speaker config fom the headunit? Can i even add the doors to the existing?

Lastly were various headunits available as options and if so are they compatible to swap out?

Any help appreciated!