hi guys i have a audi a6 avant its a 2004, i have a problem, my rear speakers and subwoofer do not work at all. iv check all the wiring behind the stereo and everything is fine there.

i took apart the whole boot and removed the subwoofer and opened up the housing hoping to find a fuse but there is no fuse in there, heres a pic of the subwoofer and what i found inside the housing, and also a pic of my stereo which is a non bose system symphony cd and cassette player, if you know were the fuse is for the amp or even were the amp is please let me know as iv searched the net for hours and no luck!!
all your help will be every much appreciated!
thanks for reading

heres the pics below