Hmm.. My next suggestion then would be to use ITunes to download the audio books (pretty straight forward if your mother could get used to it) then pop the audiobook on a ipod (he can either use headphones or pop into onto a dock to play next to him).
I use an apple ipod shuffle as when at the gym, I can feel the button I need to either pause or swap tracks without looking, but he'd have to use headphones with this as it won't dock - but it is really easy to plug into a PC or laptop and drag & drop audio files from ITunes onto the Ipod.
I've just spotted this free audiobook download site if it's of any interest:
http://www.openculture.com/freeaudiobooks
My dad's sight is gradually getting worse and he loves the audiobooks from the library, but feels the same - the choice is very limited.