Overdrive audiobooks and Sirsi?

Whatever exercise we are doing, I always learn something useful. For instance, for this exercise I learned that Overdrive's collection includes language learning audiobooks. My overall impression of Overdrive is that their interface is well-designed and user friendly, such as marking titles that are permitted to be burned to CD and offering categories like newly arrived or recently returned.

Unfortunately, they don't seem to use Library of Congress subject headings, relying on keywords. They limit the search field "subject" to less than 50 subjects. This probably means we won't be able to add our audiobook collection to Sirsi -- or, if we actually can add them to our catalog, that when you do a subject search, audiobooks will not be included in the hit list. Things get ever more complicated.