It's been mentioned, but I can't emphasize enough how much of a difference hi-passing and low-passing your tracks makes. Put a hi-pass on anything that isn't a central bass instrument (Kick, bass, etc). Try around 150Hz and increase it (not soloed) until you can hear the difference in the mix, then back off just a hair. Do the same on all of your tracks with a low-pass; You can easily low pass at 12KHz without losing anything on almost every track, and you can push it down to 7.5KHz-9KHz on guitars and other things no problem. Stuff like bass can be way lower, around 1.5KHz or so easily. Recently on my tracks, the only things that aren't hi-passed are the bass and kick drum, and the only things that aren't lowpassed are the hihat and cymbals. This will clean up "junk" frequencies that aren't contributing to the mix, allowing you to push it way louder without sounding as squished or harsh.