"""It's a plug-in for your DAW. You use it to master the track after you are happy with the mix...."""

Well, lol... I would say that's the problem.
Whatever plugin you use on your master track creates the "atmosphere" in which you have to make your "mix" sound good within. For example; There isn't a plugin that you can apply to your master track to beef up your drums that won't also effect the rest of the mix. If you're relying on your master track to make your mix sound good then, your approach is backwards. The only thing iZotope analyzes is overall Eq. If you want to beef up the drums then you have to beef up the "drum track". Of course, that also applies to all other tracks as well. Does that make any sense?