pretty sure waves platinum bundle will sort your mixdown problems, use spectral analizer and eq the fuck out of every sound you use. Dont peak at 10 on the spectral analizer im told. take low end frequencies out of sounds with the equalizers, but the best tip i can give is use decent vsts and samples for your tracks, if the source/quality is a bit shit, it will show on the final product, theres an old saying, you cant polish a turd.