ShaneWardMusic hi Shane, i know exactly what you are trying to get because i do the same thing with my gigs, some i use all my subs and some i dont use any and it feels as though i need to tweak the bottom end to give it more kick in the bottom end when no subs used,
But doing it in ST3 is not the place to be doing this.
ST3 already has so many places to control EQ and volume it is really asking way too much.
I thought the exact same thing you did than i thought about it, all my songs are setup to sound perfect through my 2 yamaha front house speakers so when i do small gigs everything is as i want it, if i have a large gig with subs, i setup my sound to get best results out of my yamahas then i use the volume knobs on the actual sub speakers to balance them with my yamahas, this then requires no more tweaking as all my songs are well balanced.
So my suggestion is when you create multi track songs always mix the multitracks to be well balanced to your fronthouse without the subs, once you introduce subs the mix will still sound great if you just add the subs to a point where in a big venue they just bring back the bass to suit the venue.
When mixing sound a lot of people dont use the features available in the correct order or way and this can eventually give them problems, like distortion or poor mixer cotrol of mixing due to wrong knobs beeing tweaked.
It should not be ST3 job to fix PA issues , the PA shuld be setup to receive a perfect mix from ST3.
I personally have a DRUM TRACK that runs about a minute, which i allways use to setup my PA, as the drums give you your full frequency range, as soon as i hear this track i know exactly if all my tracks will sound great or perhaps i need to hear more subs, its very obvious, so i just tweak my yamaha boxes to suit as they have 3 different freguency options then i tweak my subs to compliment the yamies and thats it, 5 minutes to setup gives me perfect results in any venue.
Hope this helps and wasnt too much of suck egg information but it might help others that read this.
Yes i agree what you are asking for would help those that dont spend time to do any accurate mixing, they grab a track shove it in to ST3 and expect to fix it on the run but this has a lot of problems when dealing with lots of songs you will forever be tweaking on stage by not spending the prep time in the first place, your best solution in your case is to output your sound in to a digital mixer like Xair16 or 18 have your drums and bass seperated from the stero mix and use the mixer to seperately control individual instruments you want to have a global control, this is your fix it now option.
Cheers Damir