What does the engineered hardwood manufacturer say about using cork underlayment?

couldn't you beef up the soundproofing in the ceiling on the rental unit? put something in the ceiling or crawl space?

or, are you removing the current subfloor on your own floor? if so, you could put something in between the joists before the new subfloor.

i don't know that a thin layer of cork over a plywood subfloor is going to make a huge difference.