How do I automatically loop and play a file at power up?

You can strap the rear "play" inputs of the 8-Traxx using a wire to cause the 8-Traxx to play loop a file on power up.

In order to play and loop the file, the filename must correspond to channel that you want to play.

snd00001.mp3 corresponds to channel 1
snd00002.mp3 corresponds to channel 2
....
snd00008.mp3 corresponds to channel 8.