iPod won't play with New Stereo Receiver

I recently purchased a Marantz SR7005 AVR which is equipped with a USB port for playing ipods and USB memory sticks. The receiver is also compatible with airplay. When plugged into the USB port my 5th generation, 30 gig ipod video is not recognized by the SR7005 however my even older ipod shuffle is recognised and will play. I have been told by the HiFi shop that my ipod will not play because it is too old and probably doen't have the most recent ipod firmware. I regularly update itunes and itunes tells me that i have the up to date firmware for my ipod. My question is: Is ipod firmware the same across the range of ipod models or is the firmware different for the each type or generation of ipod?