I would recommend using replay gain 2.0 calibrated to -23db this allows for more than +6 increases on slow songs or quiet backing tracks otherwise these tracks are capped at +6db on ST3
I personally use beatunes on Mac but there are alternatives
To make things easy for perfect gain staging on the input of your digital desk
I recommend setting your gain on your desk at +15db
This is based on a 3.5mm to split mono jacks
The technical reasoning for this is line level consumer cable is -10db
So a +10 db is used to compensate
And in addition the difference of -23db replay gain to -18db (which is optimum for digital desks) is 5db so this is also added on the gain
Hence +15db on your digital desks input gain