Help with planning out a Membership site

I've read through several WPMU tutorials and threads about the Membership plug-in and I've created a test site which replicates the access levels used in the guide. But I don't think I want to use a hierarchy such as Free/Premium/VIP.

I want customers be able to purchase access to separate "collections" of audio and video files. For example visitors would see the following collections available purchase:
Collection A
Collection B
Collection C

They can purchase access to one or more of these collections at any time, and without having to cancel a "subscription" to another collection. Basically I want them to be able to stack access levels. Subscriptions will be indefinite, no renewal necessary.

Can Membership do this - and if so, how? Or is there another plug in which does this better? Keep in mind that I want to be able to protect audio and video files from being downloaded or shared.