All tiers with a physical version of the game also included a digital copy. The CE box version comes with 2 Steam keys, while I believe the regular box version contains 1. Steam was used for the disk version in order to facilitate a day one patch, to incorporate changes and additions after the disks started being manufactured. You should have gotten an email from Larian about the 20th, with instructions on how to request your physical version be delayed until a second run of disks could be done incorporating the day one patch (and so removing the need for Steam).
I'm not sure which tier you are referring to, but you have 3 or 4 copies of the game, two of which you can choose the distribution method for (digital from tier and add-on), and the remainder Steam (box).
There is no way to retrieve the Steam keys from your box before it arrives.
