Is it Possible To Play Back Two or More FilePlayer Audio Units in an AUGraph?

Targeting iOS, I want to playback two .caf audio files simultaneously.

I've created a simple AUGraph comprised of two "Generator" Audio Units (subtype kAudioUnitSubType_AudioFilePlayer) connected to a multichannel mixer AU which is connected to the remote IO (output scope).

I can successfully play back one of the files with just one filePlayer AU connected to the mixer. To play back the two files I'm simply creating another instance of a filePlayer AU and configuring it in the same way as the first filePlayer.

I'm opening the audio files and then passing them into the Generator units using the kAudioUnitProperty_ScheduledFileIDs property, and the kAudioUnitProperty_ScheduledFileRegion property.

I'm checking for errors all along the way with all AU calls and nothing is returning an error. When I start the graph I get nothing but silence.

Here's the snapshot of my graph after pressing "Play":

AudioUnitGraph 0xF7DA000:
  Member Nodes:
    node 1: 'auou' 'rioc' 'appl', instance 0xf18e3e0 O I
    node 2: 'aumx' 'mcmx' 'appl', instance 0x9d72f50 O I
    node 3: 'augn' 'afpl' 'appl', instance 0x9db6ee0 O I
    node 4: 'augn' 'afpl' 'appl', instance 0x9db6fd0 O I
  Connections:
    node   3 bus   0 => node   2 bus   1  [ 1 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]
    node   4 bus   0 => node   2 bus   2  [ 1 ch,  44100 Hz, 'lpcm' (0x00000029) 32-bit little-endian float, deinterleaved]
    node   2 bus   0 => node   1 bus   0  [ 2 ch,  44100 Hz, 'lpcm' (0x00000C2C) 8.24-bit little-endian signed integer, deinterleaved]
  CurrentState:
    mLastUpdateError=0, eventsToProcess=F, isRunning=T (3)

Is there a nuance to using multiple filePlayer Audio Units that I'm missing? Is what I'm attempting to do possible in this way? Or do I instead need to create audio buffers and feed those to the filePlayer units manually?

What you have should work, but there's a couple gotchas which might have surfaced:

1. Did you set the volume parameter to be something > 0 on each bus, as well as the output? (kMultiChannelMixerParam_Volume on the Input & Output scopes).This is what I'd think the problem would be, since I believe the mixer starts with all volumes at 0.

2. Did you set the input bus count to be 2 or more by setting the kAudioUnitProperty_ElementCount property on the Input scope? (Note: since you're using elements 1 & 2 you'll need to set the element count to 3, or use elements 0 & 1 instead).