I’ve started a sketching configuration based on OT Berlin Inspire, which is admittedly a quite simple ensemble library. The configuration uses a single kontakt instance with all sections loaded, and playing techniques to select the different sections. For libraries split in to high / low, you might look into how to split channels per staff. Another possibility is to use unused treble and bass instruments, e.g. Marching Band Horn for treble and Serpent for bass. Create an endpoint with three instruments – Pianoforte, Marching Band Horn, and Serpent – and assign them each to their own instance of the Kontakt multi, and save that as a playback template. Now any time you add one of those players, it will load that Kontakt multi and you’ll have a sketching staff.