I have the 2006 Alpine head unit and I didn't need to buy an extra 'box' or anything, just a simple cable similiar to the one you connect to your computer and that's it. I believe all their new 2006 units don't need the extra box anymore, so I would go for those, works great for me on my nano, and it charges it too. The cable was like 20 bucks, definitely worth it.
Also, the songs show up on your display, and you choose what, like artist, song, album, etc. You can browse your music selection on your unit as well, works great!