Ok, well so even if your using vsti you are bouncing down to audio at some point. that shouldn`t be too much of an issue then, in temrs of the static nature of your sound.

You said you were grouping your percussion?
I would suggest each sound getting it`s own EQ treatment etc for better separation. Grouping should really only be used in special circumstances, or maybe I`ve just got what you meant all wrong.

I think essentially the poblem may well be down to a few things.
1. You are compressing all the expression and dynamics out of the mix, which could well account for the boxy sound and crushed mid range-centric nature of the mix.
2. Quality of EQ`s you are using. You might be using some cheap sounding EQ that is adding distortion into the mix.
3. Running everything too hot? Are all your mixer channels running into the red? This won`t help the sound much.