Hi. Just purchased Stage Plot Maker, and when I open the instruments tab it only has about 8 choices. I'm using this on my new iPad Pro.
This app does not include pictures for all your instruments -- only large instruments like keyboards and drums that require prior placement on stage. The sound engineers I consulted with agreed that pictures for other instruments are often distracting. You can add text labels to each of your inputs instead, like "DI for acoustic guitar."