While UPnP AV is an open and interoperable standard, it's design is inherently limited. In particular, it has a limited support for multiple media renderers and multiple control points operating on the same network.
Another major limitation is that you have to keep the control point always running while you are playing some music on your media renderer. As soon as you turned off the control point, the media renderer will stop after current tracks ends. This is because the playlist is stored on the control point rather than the media renderer.