Unfortunately, the payment processor does only that, process payments. They do not handle the downloads. Rather than attempt to handle the entire B2B library manually, a task that was overwhelming back in 2009 and would be even worse now, I am setting up an OpenCart store to sell B2B content, and it is via this that the new payment processor will operate. OpenCart enables me to add downloads and link them to the products shown in the store, so it will work just like a normal shop. It will sell only downloads.
Setting up OpenCart is going to take a while. There are quite a lot of steps and a considerable amount of learning involved. I suspect I shall set things up incorrectly and have to start again from scratch, although I may be spared some of that by the kind assistance of the owner of HD Wetting who has walked me through the early stages. There's also some good online documentation, so even a dinosaur like me will get there in the end
Even when everything is up and running, adding the entire B2B library will take some months. Once it is done it should (I hope!) be permanent. Initially, of course, I will concentrate on selling the newer items and work on the library in my spare time.