How to assign product to more than 1 quantity pricing scheme

[silken]

Hi,
I have a DVD that, when purchsed with 2 or more other 'like' DVDs gets a 10% discount. For this I have created a quantity pricing group.

But I also have a new book by the same author as the DVDs, and I want to assign a new quantity pricing group so that any of these 4 DVDs, when purchased with the book, gets a 10% discount.

How do I assign multiple quantity pricing groups to the same item?

Thanks,
Debbie