Where is the factory amp?

I have a problem with my Bose system in my Z28 I installed an aftermarket Jensen CD player and the rear seat speakers don't work. Where is the amp located? The factory unit was broken when I bought the car so I don't know if they ever worked. Also is there a way to lower the output or input on the amp? The reason that I ask is because the aftermarket cd player is putting out too much volume and its not adjustable via the unit. and I don't mean volume. The beep associated with pushing a button is ear shattering loud. Plus the amp just sounds like its getting to much input. Any help would be great, thanks!

The amplifier for the rear speakers is in the tuned box in the left rear of the car. It contains the amp for the rear sub and the sail panel speakers. The fronts have there own mounted behind them.