So, what I am doing at the moment got a little complicated. I’ll try to break it down:
I spatialize audio using my own spatializer plugin. This plugin attaches some samples that contain the location information to the current buffer when its audio callback is called. This information is just extra samples attached to the sound buffer (quite hacky). This information is later used by the SoundfieldEncoderStream.
Then I send this to a custom SoundfieldEndpoint. This means I had to implement a custom Soundfield Format. That includes implementing: ISoundfieldEncoderStream, ISoundfieldEncodingSettingsProxy, ISoundfieldEndpointSettingsProxy, ISoundfieldMixerStream, ISoundfieldEndpoint, ISoundfieldTranscodeStream and ISoundfieldAudioPacket.
When you register your own SoundfieldEndpoint with your own SoundfieldPacket you can do whatever you want with it. The problem ist you have to do it yourself. I use RtAudio (already available in UE source) to output as many channels as I want. I output all of this using VBAP, but you could use different methods.
I don’t think this is a viable method if one just wants to output some audio on many speakers. It’s quite complicated and you have to keep two audio callbacks (SoundfieldEndpoint and RtAudio) in sync.