Hello! I have an Audi 80 convertible that is 15 years old! Now I have a few questions about the speakers or the system! In the front of the amp board are 2 boxes, but there are no ones in the back! Since the box openings are oval in the back and there are no matching boxes I wanted to ask if there are any adapter rings or similar for this. Or are there other options? Thank you for your help!