Wolfram is not correctly routing audio to MOTU inputs via USB (all other DAWs and audio editing programs are able to do it correctly.
Below is a screenshot of my MOTU routing config and the nonsensical behavior of AudioChannelAssignment.
AudioChannelAssignment does the following nonsense
AudioChannelAssignment -> {1} (*plays audio out of outputs 1 and 2*)
AudioChannelAssignment -> {2} (*plays audio out of outputs 2*)
AudioChannelAssignment -> {3} (*plays no audio, same for 4, 5, 6, 7, 8*)