To route your vocal, guitar and backing track to alternative outputs, please follow these steps; 

1) Open the Setup menu and go to the Output Menu.
2) Set the Output type to Dual Mono. This will then split your Guitar and vocals to the Left and Right outputs on the device. 
3) Set the Guitar Jacks Mode to Backing Track. Your Backing track will then be routed to the Guitar outputs of your device. 

Connect all 3 sources to your Mixer and then the engineer for your gig/studio session will be able to control your guitar, vocal and backing track on their own independent channels.