Grand Staff playback different instruments

Feature request: Ability to assign and play back different instrument to top and bottom staff of grand staff. As is (per standard protocol I guess), grand staff is treated as one instrument., e.g, piano. But us jazzers typically write bass part to lower staff, melody part to upper staff, and chord symbol in between. It would be nice to hear these parts assigned to their own instrument; e.g., bass and sax. Thanks.