Could you provide more information on what part doesn't work with Shareport?. When you connect the device does shareport even detect it? Do you have a spare USB key you can also try to compare results?
If you are using Windows you could also try accessing it directly. If you press the Windows key + "r" it should open a run box. In the run box type in \\192.168.0.1. What are the results.
As for Itunes and Apple TV, this router doesn't have a built in ITunes server. I am not very Macsavvy so I am not sure what alternatives you have or if Itunes supports DLNA. If you do have a SmartTV that's DLNA or a media player that is it's a sinch. You literally can plug the USB drive in the back, connect your device to your network and it shows up right away.
Also NTFS, FAT32 are the formats that work.