Joey why do it at a gig? Do it at home as you create the backing , it’s a lot easier to spend a bit more time completing a finished backing properly than fiddling continually at gigs.
Once your tracks are properly finished in the Daw you can then fine tune them using song volume and a bit of EQ on the master EQ to perfect all your tracks in one go to suit your PA , this only needs to be done once.
The key is you need a good reference to work to, like a backing you really like and sounds good through your PA , now use that track to compare all your other tracks when finishing them in the daw , don’t fiddle with your monitoring volume , set it to a comfortable level and leave it alone, now use your ears to compare your new creation to the reference song, these very simple things make it easy to create consistent outcomes.
Making life very easy at gigs.
To finish off, have a handy master volume knob on your mixer to easily blend your backing to your live playing , this needs to be done once , from then on all you need is to use the master volume to control the overall volume of your show.
If you have a digital desk, this becomes a very simple setup , as all your click and backing tracks are consistent all you do is plug it in recall your mixers show and as long as your live instruments / vocal requirements are always the same just bring up your master volume and you are ready to go in no time.
The key is consistency of creation of your backing tracks ST3 is just a PLAYER but we are also lucky that we have full control of SONG volume/EQ, individual PLAYLIST volume and to top it off MASTER EQ, this is more that anyone expects , Master EQ is really an overkill as a mixer channel strip can suffice, but it’s great if you don’t have a mixer as some speakers have multiple inputs and some users don’t need a mixer so the built in master EQ saves the day.
Sorry for the long explanation but I want people who read this to realise ST3 is designed to suit a huge number of different ways people use it , it’s not dedicated and limited to one way of operation.
I started using your method originally and after a while realised I did not even need a click as the visual click and my ears listening to backing was enough to give me confidence to perform with backing, I am considering multitrack but at the moment I don’t see much on stage benefit.
Good luck with your level problems.
After reading your request again , are you running a mixer and are you using individual mono Chanel inputs or are you using a stereo input ?
Just use a seperate mono input to the mixer , and it’s channel fader to have volume control of the right channel which feeds both master outs of the mixer.