please have a look at an app called livetraker.
I bought the previous version that was called stagetracker 3, was a great app but now not supported anymore and after paying $100 the guy now wants another 100 euros for me to upgrade and even if I did, I use the way easier and more portable iPad to play tracks.
multi outputs is a great option but to be honest even with stereo out for my one man band gigs I could use a small multi track mixer in your app, say up to 6 channels with EQ, volume, pan for each channel, if that’s a possibility that would work magic.
while your app already is great to be able to split the drums and the bass and some extra keys/strings with a few channels (5/6) would bring the mixes of the tracks to a new level, way more work yes but way better mixes.
please look at the app I suggested (free working demo limited to 5 songs is available for both mac/Pc) and see how many of the options you could implement in ST3?
I initially hated ST3. I was one of the guys hating the queue list, and eventually opted for a refund. I paid the discount rate as I’ve got the ST2 app and after I got the refund and was following your updates, repurchased the app at the full rate again and now I can’t do without it 😊