[BusyBoxSt7]

things we need to have any clue what you mean

1) samples of your mixes
2) references to what you consider a "big" "fat" "punchy" etc mix, the words mean different things to different people.
3) a link to a website if you have it w/ pics of your room, list of other equipment, etc.

you covered the "central nervous system" of your studio but you left many questions at the very START of the recording chain.

possible factors/things that = small/bad sound to me:
-bad room? have you addressed control room acoustics?
-instruments- are you using tube amps, real drums etc or modeling/imitation stuff?
-instrument maintenance- are the guitars intonated properly
-pres- anything other than the PRE? i find preamps and converters to be more important than microphones often.
the list goes on and on, need some samples.