Thanks for the further suggestions re audio books and Ipads. The reason for looking at ebooks and TTS is that a) they are cheaper than audiobooks, b) there is considerably more choice in topic. My husband's choice of reading tends towards things like the history of the Cathars and ancient sea battles, not something you often find in readily available audiobooks - or at least not in affordable form as his interests tend to be priced at academic levels.
I will look into the Ipad, but the cost is off putting and I'm not sure how he would manage with a touch screen, but this may be the answer. Thanks for the suggestion as I hadn't thought about an Ipad being an option.