I suggest you consider simply acquiring speakers that will fit in the stock openings. If you use high end speakers you can get excellent sound. Then, put a subwoofer in the trunk with a port to the package shelf. I used a pair of ADS coax (cheapest they make and better than the best crap made by Alpine, JBL, MB Quart, and so on) 4" for the dash and 5.25" for the rear; fit just fine (rear goes in from the trunk). A 50x4 McIntosh amp with a xover and sub out is in the trunk; sounds spectacular. I have not yet put a sub in as that will add another grand to the system and, believe it or not, the midbass is strong and I don't really feel the need so far. Other speakers to consider are diamond, focal, and eton.

good luck
Carl