Link - How to make Rhythmbox et al treat a storage as a player
(See also Firefly DAAP server, first impressions.)
Rhythmbox will not initially identify the device. To get rhythmbox to see the device, you simply place a text file into the root directory of the player named '.is_audio_player' (/media/Sansa View/.is_audio_player).
You can also tell rhythmbox where to store files it transfers to the device:
audio_folders=MUSIC/
folder_depth=2
Taken from: Sandisk Sansa View on Ubuntu Linux