I've got the Pioneer plates in my truck. They sound very good for a coaxial-type of speaker, but they really sing when powered with a modest amp.
You might want to consider only installing them in your front doors.
Put that other $100 towards a 4ch amp and a free-air sub for the rear deck. With an extra $50 or so, you can get a dramatically improved system.
You'll probably notice little or no difference replacing the rear door speakers.
Just some thoughts...
BTW, the factory amp sucks. You've made the right choice bypassing it.
