The server software OverDrive uses for libraries is Adobe Content Server 4. It's quite expensive, about $6,000 to license plus about $2,000 a year fee plus a per DRM transaction fee, but I suppose could be an option for you. However you'd have to get the individual publishers to sell you the books so you could put them on your content server.
Kind of like what Douglas County Colorado did instead of contracting with OverDrive...
http://www.libraries.wright.edu/nosh...book-solution/