I understand your need to protect your IP.
My feeling is that you are already techically protecting it as much as can be done, in addition to the legal protection of your copyright. A user already has to be some kind of a logged-in member to have the URLs to the mp3's you already provide. Also, IMHO, your most valuable IP is the lessons themselves. Audio recordings of words and individual sentences, while very valuble to learners of Korean, are nonetheless much less unique, and therefore have less intrinsic value in terms of intellectual property.
Even though your flash card mechanism has some cool and unique features, it still doesn't meet my wishes in a number of areas. I can enumerate them if you wish, but the point I would like to make is that it is rare that any one product of significant complexity can meet the complete desires or requirements of it's customers, though it is a worthy goal to try (which being a software developer myself, I strive for, but know realistically that it's just a goal). The most helpful thing you can do is to provide the content in ways that customers can maximize their use of it in the most efficient way possible.
When I first started learning Chinese many years ago, my mechanism for getting flash cards was to photocopy enlarged pages from the textbook, use scissors to cut and then literally paste them on to index cards. I spent many many hours just doing this, which was a significant percentage compared against how long I actually studied the cards. Since then, my goal has been to find the most efficient way of doing that kind of thing, which now of course has been made much more efficient in our digital age. But still, the idea is to get that overhead percentage as close to zero as possible, and even the simple act of copying and pasting individual definitions into a flash card program is still way more overhead than I want to spend.
Though I've not actually written a parser for your export mechanism output yet, in theory it goes a long way in making my life easier in getting your vocabulary content into my flash card program. And in using your flash card mechanism, it really made me see the usefulness of having audio, especially at the beginning stages of learning a language. I already had that (and also video support) in my flash card program, but I didn't really appreciate the usefulness of it until I started from scratch learning Korean and using your flash card mechanism. At present, I record the audio for the vocabulary words myself, which being a beginning non-native speaker is not optimal, and of course is somewhat time-consuming. Ideally, I wish I could type just a few keystrokes to export the dialog sentences and vocabulary, and then type a few more in my program to import them, all without having to do any more manual effort of reformatting, etc.
Anyway, I wish you would reconsider, and think more like me in terms of providing your excellent content in forms that minimize the overhead for your more technical users. If you like, when I'm a little farther along, I can show you what I've done with my flash card mechanism, and point out the features I wish yours had.