While the AV or Digital Binloop can receive a command to play 1 mono file out of just the right channel or 1 mono file out of just the left channel, to achieve multi-channel synced playback, you must use stereo files as each Reproducer card drives two mono channels (one stereo channel pair) of audio. If you only have mono files created, you can use this reference to merge them into stereo files with Audacity, which is a free piece of software available for download here:
Step 1: Open your mono wav file (left track) in Audacity.
Step 2: Open your mono wav file (right track) in Audacity.
Step 3: Keep the gain the same. Pan mono wave file 1 all the way to the left (this will be your new left channel).
Step 4: Keep the gain the same. Pan mono wave file 2 all the way to the right (this will be your new right channel).
Step 5: Highlight both mono tracks. Under "Tracks" in the menu, select "Mix" then "Mix & Render to New Track".
Step 6: Select your new stereo track. Select "File", "Export", "Export as .wav" (make sure it stays 16-bit, as that is the highest audio quality the AV Binloop can play).
You'll now have your newly mixed stereo .wav file. Now the left channel will play as well as the right channel but it will be stored on your binloop as a single stereo file.
Save this single audio file to your Binloop's compact flash card, as something like "Track00001.wav".
Testing with AMI Terminal, we can easily use the S-Play All command to synchronously start audio track 1 on all of your reproducer cards that live in the Binloop. All of your tracks should then begin playing in perfect sync!