Beginning at about build 100 of J. River Media Center 14, DLNA support began to be more complete. You will need to set the UPnP Server to "DLNA".
DLNA is a super-set of UPnP. In UPnP protocol, there are three components:
1. A Device (a server)
2. A Renderer (the client)
3. A Control Point (something like a remote control)
Our UPnP Server is a "Device" (#1 above).
MC 14.0.118 added the "Controller" or "Control Point" feature, so it can start playback and control another copy of MC.
More information on UPnP can be found in the article on UPnP Server.