I've had several people ask me recently if it's possible to run background tracks and click tracks, while playing keyboards, using just Mainstage. While I've never been a fan of putting all my eggs in one basket live, you can run the entire show from just Mainstage, including tracks. Here's how to do it: 

1. Open Mainstage. Pick a concert. 

2. Grab your backing track. Make sure it's a .wav, .aiff, or .caf file, then drop it into your channel strip library. It should look like this: 

3. At the top of the channel strip library, select "Show Metronome Channel Strip".

4. This is where the fun begins. If you're running in mono, I'd recommend sending a mono track output to the front of house. To do this, insert an Audio FX by going to Utility> Gain. 

5. Now select mono on the Gain plugin.

6. Pan the playback track to the far left. It should now just be coming through output 1. 

7. Now pan the metronome channel strip to the far right. It should now just be coming through output 2. 

8. Open the playback plugin on the playback channel. Now set these controls to the following parameters :

•Sync: On (this keeps the track synced with the patch tempo and other tracks)

• Play from: start (I prefer this, since if I have to restart a song quickly, I want to start from the beginning).

• Metronome icon: on (this syncs the metronome and audio track together)

• Drop down menu: Start with play action (this will allow you to quickly start/stop the track with the press of your space bar)

9. The last thing you'll need to do is set the tempo of your patch to match the tempo of your backing track. You can set it here:

10. If you need to add other backing tracks or put in audio cues, you can simply do this process again with a new track. 

Note: if you're running in stereo, I'd recommend using a multi-output audio interface, and assign all your backing tracks to output 1-2, and your click and cues to output 3-4. 

Good luck!