DLNA streaming TO musicbox - How To?

I’m trying the whole day to stream music from a DLNA/UPnP server TO Musicbox but I’m unable to be successful.

Following setup of the network:

  • MiniDLNA server running on the network
  • Content is accessible from a laptop wired & wireless (so DLNA server is running properly)

Musicbox running on a PiB+; can stream music from the internet, can adjust the settings via webinterface or putty. DLNA switched on; upmpdcli is running.

As far as I understood upmpdcli is just a DLNA render and I need an additional DLNA control-SW, right? (although I don’t know exactly why this is needed)
So I tried to install BubbleUPnP Server on the same RPi but it’s not working properly.

Can someone tell me what and how to connect the Musicbox to a network based DLNA server and then choose the music to be played?

Normally people install BubbleUPnP on another device (i.e. their
smartphone) and use it to select the media server and the renderer and
control playback.