Put summaries of your ARGs on the DVDs!
I think that if you're going to answer questions from the show in alternate places like ARGs that only your hardcore fans typically follow, there should at least be some DVD special features summarizing them.
For example, I got a lot of people into the show, and I still hear lots of people asking "What do the numbers mean?" because most of them wanted to know that from the show. It would be pretty easy to cover this on a DVD, just put the "Sri Lanka video" on a DVD somewhere and call it a day.
Likewise with the Find815 ARG, a brief summary of how 815 was found by the Maxwell Group manipulating Sam would help out a lot. Same with any questions that are answered in the video game.
Actually, an entire Special Features menu dedicated to answers not addressed in the show would be really awesome. I hope you eventually do this.