Just a little hint for those who experiencing troubles with NFS mount in Volumio. If you has mounted your NAS successfully but the library is empty then you have problems with permissions. The case in that what Volumio trying to get access to your NAS with default user volumio instead root. All you have to do is go to /mnt/NAS$ folder via terminal and perform sudo chmod ugo+rwx %yourNASname%
Thank you for a useful post!
After houres of searching, this worked for me! You saved my day!