2005 Toyota Camry with JBL Speakers (factory amp) can I integrate it?

Surprised no one has responded yet -

I am not sure exactly what you are asking - is the Pioneer using the internal HU amp and you want to use the factory one instead?  Or you want to replace the Pioneer and use the factory amp?

CF says this in the installation details for your car:

Your vehicle is equipped with an upgraded factory sound system. We'll include a wiring harness (free with most stereos) that will bypass your factory amplifier so you can take advantage of your aftermarket stereo's extra power.

This is the Harness - http://www.crutchfield.com/S-v7Ziy8G8cmN/cgi-bin/prodview.asp?i=120701761&s=0&cc=01

I don't have details, but if you can bypass it this easily, I assume the JBL speakers are 4-ohm, and also that the Pioneer HU is more powerful than the JBL factory amp, so you wouldn't gain anything by going back to it.

If the Pioneer is not loud enough, I don't think you have an alternative except to add an aftermarket amp, but you might need to upgrade the speakers as well.