[Koha] how to classify e-books/e-readers

Hi, my library purchased a few e-readers (Kindles), which I am going to populate with e-books soon. Each e-reader is likely to eventually contain the same collection of e-books, but should of course be available for loan separately. I assume that a separate MARC record should be entered for each different e-book, but how do I enter a record (and an associated item) for each e-reader? I am sure this topic has been dealt with earlier, but I could not find specific solutions in the mailing list's thread (apologies). Many thanks and best regards, Giuseppe.