I don't usually endorse the whole stem concept but recently I had a client where the stem thing really worked well. He is a regular client and a very good mixer that usually supplies stereo mixes. On this particular project, out of necessity, he had mixed in an unfamiliar environment. I think it was an engineer friend's apartment. After talking with me early in the process, he decided to break out the mixes as stereo track, bass, and stereo vocals with effects, plus the actual complete stereo mix all lined up in a ProTools session. He was unsure of the low end and it worked perfectly for us. On about half of them I used the stereo mix. The other half it was easy to contour the lows on the kick (from the track stem) and the bass separately. On a few I eq'd the vocal without changing the ambiance by using the Massey M/S matrix plugins and inserting eq/comp/d'esser inbetween the encode and decode. Some songs only the bass/kick stuff was changed, some songs only the vocal tweaked, some both. Half the band was present for this and they had no problem signing off on the changes right then and there. It took a little bit longer than a typical session, but everybody was really happy with the results.
Dave