JBL Head Unit, can I upgrade w/out replacing?

OK, so I have the JBL Headunit with 6 discs, bluetooth, xm, and rear camera. You have to turn this thing up quite a bit to get any decent sound, and it sounds like its straining to produce any quality sound. I'm thinking a more powerful amp would help this set up. I believe it has a built in amp already, is it possible to add another amp?

I've looked at replacing the head unit, but all of the harnesses, bluetooth, & camera would cost more than I want to pay. I'm fine with the stock bluetooth, and back up camera.

Any help is appreciated!

 

I added the camera because I would not be able to use the stock one with a new head unit, right? I have an Alpine amp sitting around so that shouldn't be a big deal. So how would I bypass the stock amp? Sorry I don't know much about car audio.

 

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