I’d like to correct myself: the passage the Sixth Patriarch heard that day in the marketplace was from the Diamond Sutra, not the Lankavatara Sutra.
Hearing the Sutra: the Lankavatara
The issue for me is not whether the Lankavatara was a part of the Sixth Patriarch’s enlightenment experience; the issue is the nature of that experience. Here’s something I found under Milton Erickson on Wikipedia the other day, and I think it goes to the heart of the matter: