Has anyone taken measurements of the speaker mounting hole inside the front doors? I wonder if it would be possible to fit 8" midbasses rather than 6x9's. I don't really know of any very good 6x9 midbasses, but excellent 8" woofers are plentiful and cheap.
as long as you are not using a super deep 8" I don't see much issue there. The 8" will however sit offset from the speaker grille (unless you plan on modifying the grille) since there isn't too much room at the front of the door (the part of the door closest to the front of the car).
I say do it! where there is a will...there is a way (with money and time )
I went with a high quality 6 1/2 tri-axial. It sounds great on CDs, USB, And
AUX. I didn't replace the head unit (AM/FM still mudded even with good speakers and amplifier or subwoofer (subwoofer are highly overrated, but that is for another discussion). See original thread : general-discussion-forum/119609-upgrading-audio-tomorrow.html#post1651689
Used- Hertz HSK 163.4 3 way system with JL Audio HD750/1 Amplifier.
Yes, you typically can get better sound with a larger speaker and if 8" will fit and it is higher quality you will get better low frequencies.
to add on to what bill said, check the depth. I was able to fit my ID CTX65cs comp's with a 3/4" baffle and had about a 1/4" - 1/2" clearance from the window(when its rolled down) you can look at the spec sheet and do the math to figure out the depth your limited too.im not sure if it will be offset from the center of the grill but you may have to cut away from the inner skin of the door depending how big the basket of the 8" your putting in. Image Dynamics has a good set of 6x9's too.