1)
What do we learn from "vi'Ymei David v'Asaf mi'Kedem?"?
1.
Ibn Ezra: Like the singers were fixed before [who will be in the different Mishmaros], so they did now.
2.
Malbim: Then they fixed who will sing. Asaf and his sons were always the head singers, Also, they fixed the Shiros of praise and thanks.
