my RasPi3/OSMC is plugged to a video projector, and I would like to redirect the audio output from the Raspberry Pi to my Harman Kardon Aura AirPlay/DLNA speaker.
So far I have found plenty of documentation on how to stream audio to the Raspberry Pi, but not for my use case: streaming from the raspberry pi to a wireless speaker.
From what I have found I can forget AirPlay support, but I don’t find how to tell Kodi to find and use my DLNA wireless speaker as a default audio output, it doesn’t show up in the “Audio output” list.
If you go to Kodi, Settings > Services you can enable DLNA for several things, one of them is to allow other devices to play media from Kodi.
The idea of DLNA is that Kodi accesses media on other devices within your home network (LAN/WLAN) OR other devices (on the LAN/WLAN) access media on Kodi. The latter sounds like your usecase but it is not since it would require your speaker to ask for the media from Kodi. You want Kodi to output audio to your DLNA speaker. That is not how DLNA works, as far as I know.
Qualcomm used to have an app for Android allowing you to redirect audio to a DLNA-capable device (like OSMC/Kodi or in this case your HK speaker). But the app needed to play the audio files itself. It was not possible to play Spotify and use the app to actually redirect audio to DLNA. But it does mean it should be possible to do what you want via DLNA IF and only IF your speaker allows itself to receive anything via DLNA and play it back AND if you have software capable of sending it to your device (which is not supported by Kodi).
So that means you will have to use a cable or Bluetooth --> I used to have a HK Soundsticks III Wireless. I could play back anything on it via Blueooth, but so could anyone else in the area, the HK set did not have any Bluetooth security. One morning 4 AM I woke up because I thought there was someone in my house, it was the HK set playing movie audio, probably from one of my neighbours. I sold the HK set a week later.
I hope yours does require devices to authenticate first… when using Airplay or BT.