new audio system in a 2005 corolla

Greetings,

I recently added a JL Audio TR650 CSi to my front 2 doors in my corolla, sounds really nice, but I am still using the stock amp and rear speakers.   I am trying to get good quality, but at a good price as well.  Using the corolla's stock amp, i think is about 60 maybe 80 watts, or so (??)  isn't enough and is noticably destroying the potential of the JLs, I am split from hundreds of reviews/forums as to which I should get either a decent head unit, or an amp... since eventually I am determined to replace the stock rear speakers with JL TR's also, and then a sub even further down the road.  Should getting a decent head unit give better sound quality to the TR's in the front, or should I get an amp first, and if so what amperage??  And like i said eventually I am trying to upgrade the sound all around.  Everything is stock except the front door speakers right now.  Thanks for all the help i can get!

how much wattage can I expect to gain from a head unit such as this?  the JLs are 75 watts rms