Probably better asked in the network forum, however your Onkyo should show up in the playing now as a zone on the main window, left hand side.
You will have to enable DLNA in the media network. Working from memory you will need server and enable mc to control other DLNA devices.
At which point you should see the Onkyo and be able to select it as the zone or go to a track / album and right click and use the "send to" option
Nothing will work until the Onkyo shows up in "Playing Now"
On my den on it is seen whatever input the receiver is set to, but of course I need to select Network Audio input if I actually want to hear what is being streamed from MC to the receiver