06 Ford Explorer Speaker Upgrade

I've got a nice new 06 Ford Explorer with the Audiophile stereo (Pioneer AVIC OEM).  I'm looking to use a pair of MB Quart speakers (PCE 213) that I've had for a while but never used.

Here's what I'd like to know.

Are these a good choice for the ford explorer?  I've read that some installers use a 6x9 speaker in the front door (but I believe they have to modify the opening).

I've got to find a place for the crossovers, any suggestions here?

New speaker wire or can I get by with the factory wire already there?

I'm also considering a more comprehensive upgrade keeping the headunit (since it's also the NAV), but installing amps and replacement speakers.  Any suggestions of how I should approach such an upgrade?  I've been out of the car stereo scene for quite a few years since I had my Nakamichi tape deck, altec lansing 6x9's and alpine amps.  Wouldn't even know where to get started.  Figure my budget at about $1,500.00-2,000.00.

Thanks,

Roveer

My bad.  I'm going on an mission to see exactly what's behind my door.  Probably will be a 6x8 but I'll report back.

Roveer

OK, a little research has shown that the Ford has 6x8's in the front door.  Now, here's my question:

I've got a pair of MB Quart PCE 213's which are 5 1/4" speakers from MB Quarts "Professional Line".  These are $280 speakers. 

I understand that I can buy an adapter bracket 6x8 to 5 1/4 to make these fit in my Ford.  Question is, will these sound a lot better than the factory installed speakers considering they are actually smaller than the 6x8's?  My other dilema is where to install the crossovers, and should I replace the factory speaker wire.

I'm thinking about doing upgrades in steps, first get some better speakers into the car, then if I feel I can afford it, put in 2 amps or a 4 channel amp.  With clean source material the factory stereo doesn't sound bad, but I'd like to make it sound a whole lot better.

Roveer