the way the sql express is configured when AC installs it is setting up the security so that you just cannot install SQL tools and get in with integrated security.
I know about sql server and sql express(it used to be called MSDE). I worked with the product team( microsoft sql server) about 4 years ago.
The only way you can get in is by changing some accounts(service) and making yourself the dbo.
I would refrain people from messing around with security too much especialy on your main server. There is certian user account the client uses to get into the db. The AC user is not sql server user. I can just go on and on.
