[Hardlec23]

I would like to do this.  (It only sounds complex)

I want to plug my tablet into the Aux Input of my EWI. The music will go through my EWI, which has a cable to the Speaker/amp.

I now want to have my viewer play the back track to the song while I am viewing it

So I play my EWI to a backer track.  I can see the music and have a little moving cursor so I know where I am, and all this goes to my amp.

Easy peasy.

How?

[Zubersoft]

Are you just wanting add an audio file to play back in MobileSheets? If so, long press a song on the library screen to select it, tap Edit song to go to the song editor, go to the audio tab, tap the + icon, tap Local File to select a file on the device, select one or more audio files, tap OK, then tap OK to save the changes, load your song, tap the center of the screen to bring up the song overlay, tap the play icon on the audio player and you will hear the audio playing. You can setup the audio to automatically start playing when the song is loaded if you prefer.

Mike

[GraemeJ]

Mike, I think you missed the OP request for "I can see the music and have a little moving cursor so I know where I am".  AFAIK, this isn't possible in MSP?