A4 2.8 quattro avant

[mitch.g.]

Hi, I have a 99 S reg A4 2.8 quattro avant, it has the audi concert stereo system with 6 disc cd changer in boot, however, today for the first time I had to put the rear seats down to carry a large load. I noticed some wires that were obviously attached to something else in the boot to do with the stereo system. I've heard that my particular audi came with factory fitted amp or subwoofer and was wondering if anybody can point me in the right direction as to replacing whatever was there. Many thanks, Mitch.