^^^^ agree w/ rick3000 ^^^^^
please edit your post in paragraphs. It's been a long day and my eyes are fuzzy so I can't focus to read all your questions. Anyhow, you can use coaxials in the doors, but there is a filter in the amp that only sends lows to the doors. Unless you also change the amp, only wire up the woofer part of the speaker (you can eliminate the crossover if you'd like)
Regarding upgrading the doors.... plain and simple, just make baffles. I tried swapping 3 sets of 5.25" to replace the stock drivers. 2 sounded worse than OEM, one was maybe as good as........ Crux of the problem is 5.25" speakers by their very nature, w/out boat loads of power, simply cannot produce any reasonable low end due to size. Trust those of us who've been down this road, make the baffles (very easy to do) and put either 6.5", 6.75" or 6x9" in. With the right combinations, you can keep the stock amp so everything still will look stock but sound great (including w/ the dash drivers). All the mods will be behind the door skin and grille.
Lots of info on this topic (including DIY guides and a baffle template
) are available here, on renntech and ppbb. Use the search feature and you'll find pretty much any answer you need.
Good luck
