Samsung have their own version of DLNA so a DLNA server needs a custom profile for Samsung to make fast forward and rewind work. What DLNA options are available for the NSA-320 I don't know, if it's running Twonky 7 it should have device profile support, look in Twonky control panel under media receivers or media renderers I forget which. You will see a list of IP addresses and drop down boxes, make sure Samsung profile is tied to the IP of the TV.
If the NSA-320 isn't running Twonky 7 or worse is some unknown server then replacing the server may prove difficult.
If you want DVD's playable through DLNA without converting the video use MakeMKV or VOB2MPG both of those will extract the video/audio to a .mkv or .mpg container.