To Jimmy Akin’s credit, that article was written in 1993. Since that time, Ratzinger had this to say:
What does “the sufficiency of Scripture” actually mean? Even Geiselmann, as a Catholic theologian, cannot get beyond having to hold fast to Catholic dogmas, and none of them can be obtained by means of sola scriptura—not the early Christian dogmas of the former quinquesaecularis consensus, and still less the new ones of 1854 and 1950. What kind of meaning does talk about “the sufficiency of Scripture” still have, then? Does it not threaten to become a dangerous self-deception, with which we deceive ourselves, first of all, and then others (or perhaps do not in fact deceive them!)? In order to go on maintaining that Scripture contains all revealed truth, on one hand, and, on the other, to maintain that the 1950 dogma is a revealed truth, we would have at least to take refuge in a notion of “sufficiency” so broadly conceived that the word “sufficiency” would lose any serious meaning.
See Joseph Cardinal Ratzinger, Pope Benedict XVI, God’s Word, Scripture—Tradition—Office, Peter Hünermann and Thomas Söding, eds., Henry Taylor, trans. (San Francisco: Ignatius Press, 2005), pp. 48-51.
This portion and more is quoted on Protestant blog
here.
As I stated previously, I think the best we can deduce from Ratzinger/Benedict is that he’s ambivalent towards the idea of material sufficiency.