The Joey does not have a tuner so an EHD would do nothing.
You don't need a tuner to play back existing media. I would think most of the important hardware is already in the Joey.The Joey does not have a tuner so an EHD would do nothing.
So the USB port has no use to the consumer?
It will take the wireless dongle and attach to the network, which IIRC will allow full DLNA from the Joey.