If you create a login username in ms SQL and give it sysadmin rights do you have access to everything in the database? or do you still have to map a specific database?
Login with sysadmin rights have access to all the databases even if you don't explicitly grant permissions.
[Rhetorical]What happened when you created the sysadmin login without any mapping?[/Rhetorical]
My point being that when you have questions like this, give it a try and see what happens. Then if you need clarification or elaboration, we'd be glad to lend an ear...and a hand.