I was using SSD4 on a track and the drums where played via a trigger kit by an excellent drummer but they were being buried by the track so I set the multi outs to do a pre mix on them thinking they where gonna be a lot of work, but as soon as the went out there own outputs wow they really open up!
Greater dynamic range perhaps?
Everything is just much clearer, i mean i would always separate them at the end, but I didnt know the stereo out from the instrument was choking them that much.