Brett, i'm sure you know that in standard audio systems in most cars, the speakers are powered via the amplifier in the headunit (a 'star' configuration).
The Bose system is a little different in the fact that the headunit has no amplifiers. It is in fact sent 'line level' to the rear of the car where the external amplifier is located (under the parcel shelf

). The signal is then sent around the car to power the speakers and (hopefully!) subwoofer.
That is in its simplest terms but should help you to put it right. If the factory system is restored, it should sound rather good. If somebody has been tinkering (look for evidence of cut carpets, chopped wires, thicker speaker cable etc.) it may be a case of building a new system from the remnants of what is there, which should also sound mighty fine

If there's anything we can help with please post up. (In the 'ICE' section as well preferably)