I guess "Bonjour" comes with an API but to be honest I don't know where you can find it and if you would be able to do so...
However the previously mentioned plugin works like a charm and does exactly what iTunes does (but in Winamp, which is cool ;-) ).
I just have to select my amp in a dropdown then voila, music plays on my receiver and its controller sends commands through the network to change track.
I 'll check if the "Send to device" context menu in Windows is able to do the same thing with a huge playlist.
Edit :
- Cannot change the track with the receiver's controller with the Windows native DLNA function.
- Not able to set a random playlist.
Through Kodi, unable to chose a folder to send to my receiver.