Hi, you desperate both!
You cannot do anything about the folder structure!
The DLNA thing on the NAS is very simple (maybe it is a general weakness of the DLNA concept?).
Whatever your folder structure will look like, will be complete ignored. The NAS simply scans all folders and builds up 3 collections in a data base: Photos, Music and Video. It does not matter where the original file is located, it will be placed in one of these 3 categories.
You can call you media folder "foo", "bang" and "zap", and they will end in "photos", "music", "video" just because of their content, not of their name.
The overall implementation of DLNA in the DNS-320L is very basic. So don't expect too much from it.
On Management --> Application Management --> Multimedia Services you find the button "refresh all" on top of the Multimedia Shares list. This invokes the rescan automatically.
In case you like to reset the databas, I'd first try deleting and reloading the entries in this list. It is not necessary to clean the entire RAID...
The update of the Multimedia Database (once it is initialized the 1st time) happens automatically when you copy files in one of the shared folders.
Good luck, gents!
Mausschubser