Even if they won't repair it free of charge, they should be able to get you the name of a service facility who might be able to furnish the information you need for AE. If nothing else, you can start a paper trail to furnish to American Express to help in substantiating your claim and problerms.
In any case, Onkyo can probably be more help than we could.
but, be aware that you will probably have to foot the bill for an estimate up front and hope AE reimburses you for it.