Seems to me like sidechaing things like that is a complicated and long workaround for a problem that should not exist. Thats why there is an engineer present, to make the necessary mix changes. What if things start trigeering your chain when they aren't supposed to? Then the whole mix suffers. One quick solution is to buss things out a bit. Say drums in a buss, instruments in a buss, vocals in a buss. You can use the vocal buss to push the vocals over the top a bit, or use the others to duck the rest a little. If you ahve VCA's, you can use them to break your mix up even further since you can use them like a buss in the sense that they control a group of channels but you can use 1 VCA instead of 2 busses and still keep a stereo image. Not only that, but VCA's are "stackable" in the sense that you can use them sort of like groups and break things up a bit, but you can also assign something like VCA's 1-7 to VCA 10 where you can still change individual VCA groupings on 1-7, and then also use VCA 10 to be a master for the other VCA's which allows you to duck all instruments at one time from 1 fader. Basically, in over 1500 shows from small clubs and bars to large arena's, I have never seen the need for this type of side-chaining.