Ps. When I say that "a room is available" I mean that if you can see it via Amtrak.com by pretending to make a paid booking, then you can get it via AGR. Just be sure to get off Amtrak.com if it is the very last room, as you could be holding it.
If you enter 8 people traveling on Amtrak.com, then it will show you if there are 8 roomettes or less left.