When using VoiceProcessingIO audio unit with voicechat audio session mode to have echo cancellation, I can't play audio in stereo, it only allows mono audio. How can I enable stereo playback with echo cancellation? Is it some kind of limitation? since it isn't mentioned anywhere in the documentation.

I’m developing a voice communication app for the iPad with both playback and record and using AudioUnit of type kAudioUnitSubType_VoiceProcessingIO to have echo cancellation. When playing the audio before initializing the recording audio unit, volume is high. But if I'm playing the audio after initializing the audio unit or when switching to remoteio and then back to vpio the playback volume is low. It seems like a bug in iOS, any solution or workaround for this? Searching the net I only found this post without any solution: https://developer.apple.com/forums/thread/671836