To clarify, the remaining space of your sd card is available as a Samba share:
ian@StudyComputer ~ $ smbclient -L 192.168.2.222
Sharename Type Comment
--------- ---- -------
Internal Storage Disk VolumioKitchen Internal Music Folder
USB Disk VolumioKitchen USB Music Folder
NAS Disk VolumioKitchen NAS Music Folder
IPC$ IPC IPC Service (Audiophile Music Player)