I have an Audiocontrol 6xs that is connected to the pre amp lines on the bose amp in the rear of the car and this worked fine for 3 1/2 years or so. Recently the setup stopped working.

I was not sure if it is the amp or the 6xs or the car. If I connect a iphone with a headphone to rca converter and set it to max volume and connect it to the 6xs with very high gain I get the bass playing out. The radio lines are usually I connected to are usually sending out signals that are around 2 volts but when I connect it to the amp or 6xs I get nothing. Does anyone have any idea where the issue could be? I dont think it is the 6xs or amp simply because connecting the iPhone works but I have no idea at this point.

Should I connect a different amp to the 6xs and try?

Forgot to add all the speakers work just fine inside the car.