[Zubersoft]

As skip is mentioning, you can long press a song on the library screen to start the selection mode, and then you can select all of the songs you want to add at once to a setlist by using the overflow menu at the top right. You can filter the songs first if you want, start selection mode, then use the select all button in the floating toolbar to save time. Likewise, if you edit the setlist, you can filter the songs on the right then tap the add all button to add them all in one shot.

Mike