Issues with background cmvocals useing Stereo Imagery

 I have had a ongoing problem with getting my playback during a stereo imagery session  For one I can't get my background vocals remaining and deleting lead vocal only. My adaobe works sometimes and sometimes it don't. The playback before I process the session does not sound like the mp3  It should play and sound exactly like the cd or mp3 I am recording on stereo imagery. Can anyone help ??