To be honest (and I am sure Jim will shoot me down if I am wrong) I think you will really struggle to get satisfactory multi-room sync with DLNA or with JRiver with multi-client, single server. It works great for playback of different music in multiple locations, but for sync'd playback...not so much. Frequently when I have tried, sync has been seconds out.
As well as using JRiver for library management and viewing/listening on our main living room TV I have multiple Squeezeboxes (Radios, Touches and Squeezeplay). I use those mostly to access the music library outside the living room, via Logitech Squeezebox Server running on the same PC as JRiver and SqueezePad for Ipad playback and control. The "real" Squeezeboxes sync "perfectly" (you can even configure two radios, which have only a single speaker, to act as left and right channels for stereo). Squeezeplay on a PC can exhibit a slight "echo" if I stand equidistant between it and another device, but it is fine, and far far superior to anything I've been able to achieve purely with DLNA/JRiver.
(p.s. I don't think it is JRiver's fault, I just don't think the control mechanisms are there outside of a proprietary hardware/software environment.)