Since last September, BandHelper and Set List Maker have supported app shortcuts, to quickly jump from the set list view to another app. You can use this feature to jump to a mixer or effects app or anything else you want to use along with BandHelper or Set List Maker on stage.
To use app shortcuts, you need to enter the desired apps in Settings > Apps. On iOS, you will need to enter the app's name and URL scheme, which you can get by asking that app's developer (not all apps have URL schemes, but the app developer might add it if requested). You can also try searching
handleopenurl.com to see if the scheme is already listed there. On Android, you need to enter the app's package name, which you can get by installing the
Package Name Viewer app or looking up the desired app in the Google Play Store and looking at the id at the end of the URL.
Then you can add App Button or Multiple App Buttons to your song layouts to display a button that opens that app. You can also open defined apps by mapping a remote control action to the app number, or by recording a button press as part of an automation track.
UPDATE summer 2019: The handleopenurl.com has been shut down. I'm not aware of another online directory of URL schemes, so you will have to use trial and error, or contact the other app's developer to get the URL scheme.