Mmi problem

I have a 2004 Audi A8L and my MMI stopped working....so I bought the Optic loop tester and checked my CD changer, Navigation and Radio and when I checked my amp found out that the AMP was bad.....once I unplug the optic wire from the Amp everything started to work but no sound.So I ordered a amp from Ebay with the same model number and that did not fix the problem.Could the amp be bad???Any suggestions.







Thanks

Dave