There is a book of walks which Andrew has ordered, to be delivered chez David. With any luck it may even arrive before the trip. I also found a shed load of web sites which I sent to Andrew, unfortunately none of them was of any use. And the 'forthcoming' English guidebook isn't published yet (and probably never will be, as their web site was last updated in 2006).
We've also got a map or two of the national park on order, if they're of the usual Spanish quality then they'll also be of limited usefulness.
In short, there's probably something out there, but we'll probably only find it by chance