I know I am going to get slammed here by some but the approach I am taking more and more is to get the mix as close as I can to how I want it to sound, then apply a mastering compressor on the main buss and tweak from there. That way by the time I get to the final mastering stage that will get burned on cd's there are less surprises and the outcome is more predictable. Now to clear some things up I work a lot with purchased backing tracks and then add vocals on top of them so most of the time I do not have individual instrument tracks to work with. Sometimes I get a stereo music only track and a stereo drum track to work with but that is about it. The ability to go back and fix individual instrument tone and volume is not an option. I have to take what I have and shoot for the best OVERALL sound and search for a "sweetspot". So I guess I am kind of remastering the music tracks and adding/blending the vocal tracks on top/with the music. If I were working with 48 individual instrument and vocal tracks [ and I have] I would do it differently but for these projects it seems like I get the best overall sound by using mastering compressors during the mixing stage. I will continue to experiment with both methods but have to go with what sounds best in the mean time.