I had the similar problem with Varispeed node. I have several varispeed nodes connected to several buses of multi mixer. This multimixer node was connected to RemoteIO node. And sound was not playing. But then I've added converter node (AUConverter) between multimixer and remoteIO and set stream format property:
result = AudioUnitSetProperty (convertUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, 0, &stereoStreamFormat, sizeof (stereoStreamFormat));
stereoStreamFormat - this format is used in my app for all multimixer buses.
So I've believe the problem is in this format:
node 2 bus 0 => node 3 bus 0 [ 2 ch, 44100 Hz, 'lpcm' (0x00000C2C) 8.24-bit little-endian signed integer, deinterleaved]
If you add converter node and set up it's stereo format you should see:
node 2 bus 0 => node 3 bus 0 [ 2 ch, 44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]