Do this... .
I put boston acoustics speakers in and the rears take round 6" i think and the fronts are 6 x 9"
now the rear, you need to put the frame of the plastic speaker behind the speaker itself to not bottom out on the metal, then screw down, they have the 2 wire system for hookup... .
On the front, the 6 x 9 fits into the factory hole just fine but what the infinity system has is 2 small amps, one at each front speaker. This amp is bolted to the speaker. I unbolted it, then it has the 2 wire pull-offs for it too. Now when the amp is bolted to the speaker, the base of the speaker is the heat-sink for the amp so you need to bolt on some metal to the amp. Then hook up the wires to the new speakers and I used a zip tie to hold the amp up in the door-frame area to a brace or something.
This will make the system sound marginaly better, the amps i figure are not very powerfull so you might want to have a shop convert the big bulk of wires coming out of your stereo to RCA jacks so you can run it to a 4 channel amp and sub-woofer then to the speakers and it will then be a kickin' sound. I was quoted
$500 for the amp and conversion. add to that the sub and the enclosure which they make 2 kinds, one goes under the rear seat for 2 sub speakers, the other is a center seat replacement for 1 12" speaker (that's $500 in itself)
So what ever you want to do, I did the speakers for now, then I might do the conversion later.
Hope this helps
Eric