Using RFID-tagged physical objects to represent the audiobooks is an interesting twist. Why did you decide to do that rather than add "next book" and "previous book" buttons, and use text-to-speech (or even pre-recorded audio files) to tell him which book is currently selected? After all, your approach increases the amount of maintenance your brother has to do, and makes the whole assembly a lot bigger.
EDIT: I'm also curious about which products you looked at and why you rejected them. For example, did you look at any dedicated talking book players, such as the Victor Reader Stream or the BookSense?
That's a valid question. I wanted him to have physical, tangible books. A reader like the Victor Reader is, for someone who doesn't use technology, a mysterious box where the books are hidden behind buttons. I was afraid that this type of solution would discourage him. I may be wrong, but the impression I got from the existing products was they had a learning curve that my grandfather, at his age, wasn't willing to take. With his current reader, his books are actually book sized. He can have a pile of books he finished reading. There's something more "real" about it.
It doesn't actually require a lot more maintenance, except putting the titles on the "books". Other than that, we keep reusing the same cards.
EDIT: I'm also curious about which products you looked at and why you rejected them. For example, did you look at any dedicated talking book players, such as the Victor Reader Stream or the BookSense?