Answer
باسم الله والحمد لله والصلاة والسلام على رسول الله وعلى آله وأصحابه ومن والاه
Wa’alaykum Salaam dear brother. May Allah bless you and increase your knowledge. Ameen.
Kash-shaaf is definitely a book of tafseer that fits in the advanced range of tafseer books and a book that some researchers and advanced students, if not many, have difficulty taking a deep understanding from given the intensity showcased by the author when presenting his explanations.
There are two books which I would refer to, as advised by my teachers, in order to learn the deeper meanings of alKash-shaaf, and they are;
1. atTahreer watTanweer of the famous later scholar Taahir ibn Aashoor (May Allah shower His mercy upon him)
2. The Tafseer book of a well-known later scholar, Abu asSa’ood, which is known as Irshaad alAql asSaleem.
And Allah Almighty knows best.