The RSS feed from the HTML module has a very different format as compared to the one expected by itunes. So that will not work.
Your best bet is to get a podcast hosting provider where you can load the file and they will provide you with an RSS feed.
There are many hosting companies like that for instance Lidsyn is one that I have used in the past.
You may find this article interesting:
Besides that, if you want to self host your files, you will have to get a developer to code your own feed from the site as I'm not aware of a module that provides the itunes rss feed.