I'd like to hook up my external speakers to my airport extreme base station to play my itunes over the network. Since there is only a usb option available, is it possible to use a usb-to-headphone jack for the set up? Like the one on here?
Yes. USB hubs connected to printers and HDDs. It may possibly be used to power USB powered peripherals (fans, lights, etc.), but I haven't tested nor researched this. Any other USB devices will not work. It's a router, not a computer.