ginacc The output level of ST3 should be easily compensated by any large venue mixers that have a sound engineer that knows their job,
The issue is how far does your unbalanced signal need to run to either the di box which converts the signal to a balanced output to travel longer distance , as I said instead of needing a DI box use a little mixer which also gives you balanced output at standard line level to feed to any venue, plus it gives you some on stage control to turn up or down your backing track easily without needing to bother the venue’s operator if they aren’t on the ball, either way you need to have your own DI box , a mixer or a digital interface to give the venue a standard balanced out signal , as I said before the volume of ST3 is handled by the trim pot of your main mixers output and should not be an issue.
It definitely has not been an issue by a lot of users it’s your choice how you want to simplify it , I also am or was in your shoes for years in my band and know exactly what you are trying to achieve but I also am an electronic technician and a sound engineer as my bread and butter jobs, my favourite saying has always been keep it simple 😂
Just another thought!
Are all your songs recorded at the correct levels in the first place or are you using the EQ where you drop levels to EQ bringing down your overall levels on top of the -6db Peter has dropped in the design?