AVAudioSinkNode multiple channels

I am using the new AVAudioSinkNode to get audio samples from an input in real-time. I have this successfully working for a 2 channel device. I am now testing on different hardware devices, and have encountered an issue where the console is reporting too many buffers. The format of the device appears to be a 70 channel (24channel in class compliant mode) non interleaved device. I am assuming that as this is meant for real-time applications, there is a limit to the amount of buffers that this can use. Is there a way that I can stream just one channel of this input into my sinkNode? Ie, I would like to specify a single channel that I would like to capture. Until now I have been manually deinterleaving in each callback. As the error occurs in the callback itself, not in the ussr block, I cannot use a AVAudioConverter within the callback. Please can someone suggest a method?