Hi Peter - it took me a long time but I stumbled upon the reason I couldn't adjust volume on the individual tracks and I wanted to leave this solution here for others.
Forever (since we began using StageTraxx in the fall of '22, we've had extremely LOW volume output, no matter what I tried. And, like I said above, we could NOT adjust the volume of individual tracks at all.
Then I saw someone suggest that volume issues could be fixed by turning off the "Combine USB & Headphone Outputs" option. I never knew what that button did so I left it ON by default. Well, turning that OFF immediately fixed ALL the volume problems. Suddenly we had significantly more volume output AND the individual track volumes could be adjusted. I never saw anything about this mentioned in the support manual - I just saw someone mention this in another volume-related thread. But that totally worked!
For reference, the device we use is an iPad 9th generation with the headphone jack out.