Oliver Peters has written up a primer on why and how to create audio splits and stems in Adobe Premiere Pro.
He writes, “When TV shows and feature films are being mixed, the final deliverables usually include audio stems as separate audio files or married to a multi-channel video master file or tape. Stems are the isolated submix channels for dialogue, sound effects and music. These elements are typically called DME (dialogue, music, effects) stems or splits and a multi-channel master file that includes these is usually called a split-track submaster. These isolated tracks are normally at mix level, meaning that you can combine them and the sum should equal the same level and mix as the final composite mixed track.”
Read the full story here.