What's the best way to play 2 or more channels in sync?

First, assign the channels to a group using the Binloop Config software or front-panel interface.  Name the video files that will be playing in sync with the exact same file number and copy them to each channel's compact flash card.  Using either the Serial, Ethernet, or Timecode control interface, send a Synchronous Play command to the group in which the channels are assigned.