This is a cheat sheet of examples using SOX to do various common sound file conversions. If the .AU file doesn't have a proper header, you'll need the second command line. Note that you'll need newer SUN sound hardware to successfully play these files. VOC has a similar problem.
Recent models support CD-quality sound.
When you copy the file to the Mac, you'll have to set the sample rate by hand. Just convert file format without making a disk file.