I vaguely recall that at least one of the major brands may require the dock accessory to work with USB.
AFAIK, the only workaround would be to use iPod (headphone output) -->> (RCA L/R input) Yamaha. Again, that's if my supposition is correct that the dock is required ;(.
Try asking @ AVS forum too.
Newly purchased receiver and suddenly the USB port on the front of the unit does not recognize devices such as iPods or iPhones and does not charge these devices either...