Handling Multichannel Audio

I am currently in the middle of reproducing the Handling Multichannel Audio example of Session 507 at WWDC15. I created a 6 channel wav file and tried to play it with my 6 channel audio output hardware (HDMI connected to a 5.1 AV receiver). Quicktime Player can play the 6 channel wav file without any problems. So, I created the following test case:

- (void) play
{
    self.audioEngine = [[AVAudioEngine alloc] init];

    AVAudioOutputNode* outputNode = self.audioEngine.outputNode;
    AVAudioFormat* outputHWFormat = [outputNode outputFormatForBus:0];
    AVAudioChannelLayout* hwChannelLayout = outputHWFormat.channelLayout;
    AudioChannelLayout* hwLayout = hwChannelLayout.layout;
    AudioChannelLayoutTag hwLayoutTag = hwChannelLayout.layoutTag;
    AudioStreamBasicDescription* hwStreamDescription = outputHWFormat.streamDescription;
    AVAudioChannelCount hwChannelCount = hwChannelLayout.channelCount;

    AVAudioMixerNode* mainMixer = self.audioEngine.mainMixerNode;
    mainMixer.outputVolume = 1;

    [self.audioEngine connect:mainMixer to:outputNode format:outputHWFormat];


    NSURL* url = [[NSBundle mainBundle] URLForResource:@"seg01" withExtension:@"wav"];
    NSError* error = nil;
    AVAudioFile* audioFile = [[AVAudioFile alloc] initForReading:url error:&error];
    AVAudioFormat* fileAudioFormat = audioFile.processingFormat;
    AVAudioChannelLayout* fileChannelLayout = fileAudioFormat.channelLayout;
    AudioChannelLayout* fileLayout = fileChannelLayout.layout;
    AudioChannelLayoutTag fileLayoutTag = fileChannelLayout.layoutTag;
    AudioStreamBasicDescription* fileStreamDescription = fileAudioFormat.streamDescription;
    AVAudioChannelCount fileChannelCount = fileChannelLayout.channelCount;

    AVAudioPlayerNode* player = [[AVAudioPlayerNode alloc] init];
    player.volume = 1;
    player.pan = 0;
    [self.audioEngine attachNode:player];

    [self.audioEngine connect:player to:mainMixer format:fileAudioFormat];

    error = nil;
    [self.audioEngine startAndReturnError:&error];
}

Upon startAndReturnError: in line 37, I get the following error logged into the console:

required condition is false: nil != channelLayout && channelLayout.channelCount == asbd.mChannelsPerFrame

I checked everything, but I can't find the problem myself.

fileChannelCount == 6 and hwChannelCount == 6

fileStreamDescription->mChannelsPerFrame == 6 and hwStreamDescription->mChannelsPerFrame == 6

Actually fileStreamDescription and hwStreamDescription have the same values in all fields.

Now, ChannelLayout is a bit different. The hwLayout contains 6 AudioChannelDescriptions and a channelTag of 0 and fileLayout contains 1 AudioChannelDescription and fileLayoutTag is kAudioChannelLayoutTag_MPEG_5_1_A, but I don't know if that's the problem. Does anybody have an idea?