If memory serves me right, Vuo deals only with 48 kHz audio. If that is still the case, the 32 kHz limit of the C922 could explain the problem.
Maybe if the audio goes through a virtual audio interface like Blackhole or Loopback, the OS will be able to resample the audio stream to 48 kHz before sending it to Vuo.
How many channels in your files? Because "Mixed Samples - A single audio buffer consisting of all channels added together." So... Two stereo files would be four channels added together?