i'm not posting a reply because i can help with the door depth , but rather i can throw an idea your way with adding room for your speakers, alot of the custom audio guys up here use MDF fiberboard ( that stuff they use all the ime on those home re-do shows like trading spaces)

its fairly cheap to buy and very easy to work with to shape with a hand grinder/sander, your imagination is all that keeps you from designing some cool risers for your speakers, then you can cover them with some speaker box material to finish them off.