That is a reasonably old Renderer. 2012 or so? As the manual says "You may not be able to play back some content with DLNA CERTIFIED products", I would assume that it may not be fully DLNA compliant.
indeed why does it mention DLNA servers in relation to an attempt to configure a renderer?!
Because a Renderer needs to be associated with a specific DLNA Server, so that the server can be configured to match the Renderer's capabilities. For example, one Renderer may be able to play native DSD, FLAC, APE, etc., doing all the decoding and rendering, while another may only be able to play PCM, in which case MC needs to do the decoding. When there is only one DLNA Server configured in MC, it is automatically associated with all Renderers. If there are two or more, you need to actually tell MC which Server to use with each Renderer.
As I am led to believe the way to compensate for broken implementations of DLNA renderers is providing it with a stream and putting lossless formats on it (mp3 has frames and padding which makes things harder. but not impossible).
DLNA is a file based technology. Files are sent to the Renderer, not streams. So gapless playback is supported when the Renderer can be told what the next file will be. That is done using the SetNext function. Your Renderer is broken if it doesn't support SetNext, so it can't support Gapless playback.
Well, that is my understanding. I could be wrong.
Download and run
AndrewFG's Digital Media Renderer Analyser, and confirm what your Renderer supports.
http://www.whitebear.ch/dmra