My apologies. When I first read your posts asking about gapless over DLNA, I assumed you were using JRiver Media Center as I am, i.e., as a Digital Media Controller to pull music from my library and send it to a Digital Media Renderer, either my Yamaha RXA3040 AVR or Oppo BDP103D, to be played. In this configuration, JRiver controls the playback including gapless *if the Renderer supports gapless over DLNA*.
I reread your posts and realized that you are using JRiver as a Digital Media Server to make your NAS library available to your Digital Media Player (Oppo). In this configuration, the Media Player pulls the music from your library and controls the playback including gapless. According to the following link, Oppo only supports gapless for music files stored on USB flash drive(s) and external USB hard drive(s).
Since your NAS library is accessed over a network, it doesn't qualify for gapless playback.
I'm not an expert in JRiver or DLNA, I'm just passing along some info that I've been able to piece together about both. For more info about Digital Media Controllers, Renderers, etc. please see https://en.wikipedia.org/wiki/Digita...etwork_Devices
As far a gapless playback is concerned, keep in mind it only removes pauses between tracks. If the track contains leading and/or trailing silence, gapless doesn't do anything to strip that out, so there still appears to be gaps between tracks.
In my JRiver configuration, I have my Oppo defined as a Renderer only to play SACD and hi-rez 192k files. For all other music files, my AVR (which does support gapless playback over DLNA) is used as the Renderer. Up until today when I researched this stuff, I thought my Oppo was also supporting gapless over DLNA, but it does not.