When I try to view WAV files with more than two channels, AudioThumbnail only shows the first two. The number of channels in the source is reported currently and affects the layout, but no data is shown for channel numbers < 1. I am reading the missing channels just fine using an AudioFormatReader elsewhere in my app.
To reproduce: run demo app built from current tip, select "File Playback" demo, view a WAV file with >2 channels. Here is a small 4 channel one: http://madronalabs.com/media/temp/guiro.wav [1.4MB]