The first upload (5.1ch_test_file_side.flac) is a 5.1 audio file using the Front: L C R, Side: L R, LFE channel mapping layout.
The second file (5.1ch_test_file_rear.flac) uses the Front: L C R, Back: L R, LFE layout. It was created by encoding the above file to AC-3 then back to WAV using ffmpeg.
[EDIT: Uploading appears to be broken for me (Firefox 42 and Chromium 45)]
[EDIT 2: My mistake - I was having an early-morning-moment]