It's too soon to tell. One thing is certain: cutting costs is on the top of the list. It always is in these modern roll ups. If cutting costs becomes "cheapen the product" Mac is doomed to Marantz's fate.
Alternatively; If there are economic efficiencies to be had- ie: sharing buying power, advertising discounts, etc. it would be good for Mc assuming it keeps it's corporate culture.
I'm hopeful that Bose puts a slug of cash into Mc and Mc improves their product offerings and ups their quality.
Sometimes a bespoke brand is a status acquisition and not a profit play ie: Acora buying Audio Research.