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Welcome!- What region are you located?
Please feel free to post here.
This model DSM is no longer being supported however we can try to help you out as best as we can. The product is a bit old.
You might try the user manual and review to see if there is any information regarding this configuration:
http://support.dlink.com/ProductInfo.aspx?m=DSM-320I don't have any experience with this particular model. I do have the DSM-380 (BoxeeBox) and it does stream DVD and BluRay. I now use .MKV for my container for all video files.
Might look in the menus for file server location or file library location or resources where you can maybe have it connect to network shares. Be aware that the wireless on the 320 is only 54Mb and that speed is fairly slow and you may see some lag or buffering in video streaming. If the unit has LAN wired connection, then this would alleviate that and I recommend using LAN wired connections when streaming always.