Hey guys. I put some MTX 6.5's in my front door panels. Sound better. But here is your answer to why the stock speakers may have sounded louder if you already don't know. Those infinity stock speakers are 2 ohm speakers and all the speakers you are looking at are 4 ohm. So that means there isn't as much power going to your new speakers.
You can buy new 2 ohm speakers but they are spendy, at least what I have seen. Best thing to do if you don't mind rewiring is to buy new speakers and then a new amp and hook them up that way.
Also, if you buy from Crutchfield, I believe they include all the mounting brackes and speaker wire direct plug ins for free. But shop around, you can find speakers cheaper other places but they usually don't include the brackets if you need them. Not always the case, but sometimes.