You can retrieve the channel<->speaker layout using kAudioUnitProperty_AudioChannelLayout, there's a commented-out block in the catest.c.txt I posted that uses it. If it's easy for you to assemble/swap samples to match that layout, that's probably the best way. If not, that's the situation I'm in, kAudioOutputUnitProperty_ChannelMap should work but I can't figure out why it doesn't.