First are you 100% certain NAS is running on the B2 ? If not go into the B2 menu system and check.
Next Open the VLC app on your phone .
1. Now on the VLC app make sure that you tap the casting icon on the top bar .Then you can proceed with the selection of the files you want to cast to your smart device
2. tap the network icon on the bottom bar of the VLC app
3.this displays "file servers" so navigate to "BRENNANB2"
4. Enter "root" and "brennan"
5. on the top right of the VLC app click "connect"
6. The b2 Music Folder will now be displayed
7. Navigate to the file of the music you wish to cast and the track will play