just done the same on my 156, fitted JBL GTO627 2way 6.5"/16cm in the rear, these fit straight in the plastic basket when you remove the old speaker. in the front infinity reference 6020cs 6.5" components, again fit in the basket when old speaker is removed. you might have to cut away a small piece of the basket if it's in the way.
REAR... the speaker wire has a yellow plug on the speaker end, that clips off and the spade connectors will fit the new speaker.
As above plus you have two wires for the front, one for tweeter and one for mid/sub, you only need the mid /sub one (just tuck other away) connect this speaker cable to the crossover and run wires from the crossover to the tweeter and the mid/sub
Cost me about £70 for both pairs and sound superb :thumbs
No need to remove door card, remove grill and undo screws holding speaker and remove.