As you noted, your two biggest concerns are fire and theft. Off-site storage has already been addressed and is probably your most secure option, but it has limited space and speed. For a 2TB capacity, you may want to look at business packages instead of home computer packages.

For onsite storage, you will need a media and burglary rated safe ($$$). A second option is a media rated only box (i.e. Fireking Mediavault) and rely on file encryption and hiding it to deal with the theft issue.

A combination of both are going to be the safest. And remember, encrypt everthing that could be stolen or hacked.