>reducing the frequencies that the vocals stand out on...
If you had access to the singer, here's an idea: Have him/her sing all the notes in the song (trying to EQ the voc as similarly as possible, and matching the tuning is important too) onto a .wav file. Use the CoolEdit 's noise reduction and get a noise profile of just that vocal. Save the profile (or just hit close) and apply noise reduction (w/ that profile loaded) to the old mixdown..
An easier way is to do the opposite: Take the whole song .wav and cut out all the sections with vocals. Now use that as your noise profile selection and applying it back to the whole song using the "keep only noise" setting.. This should do its best to keep all your music frequencies there and, assuming the vocal is different enough, should help to reduce it.