I've streamed music from my DS209... it's a bit complicated and not something that I could get to work from Flash widgets directly.
1) On the DS209, I enabled NFS and setup a /etc/exports file with
2) On the Chumby One, I ran these commands
mount -t nfs -o ro,nolock,noexec,intr <ip of DS209>:/volume1/music /mnt/music
3) I can then stream individual songs using the btplay command with a full path to the music file, e.g.
btplay /mnt/music/Music/Flight\ Of\ The\ Conchords/The\ Distant\ Future\ EP/06-Robots\ \(Live\).ogg
4) I can also do a symlink from /mnt/storage into that /mnt/music tree to make certain albums/artists appear as if they were in internal storage. However, I found that I had far too much music to actually mount the whole tree in /mnt/storage as that would make the "My Files" sound widget take too long before appearing and starting random playback.