I tried downloading all lessons as directed in your post-purchase e-mail. Unfortunately:
(a) The iTunes interface has changed, and there is no longer a way to download everything at once. Theoretically you can get around this by selecting the entire feed and downloading. This crashed my iTunes, though, and it took a lot of work to get it up and running again.
(b) I can't see all the lessons that are available on the website in the feed. I'm working through Lower Intermediate Season 6, and there are no lessons past lesson 25 in the feed.