How to add a second administrator to Business Contact Manager for Outlook 2010?

Question

Outlook

On the PDC server Windows 2008 R2 Standard Rus, MS SQLExpress 2008 R2 "Business Manager for Microsoft Outlook 2010" is installed .
If on the PDC itself via the " Business Contact Manager for Outlook 2010 Database Tool\ServerWizard.exe" ("C:\Program Files (x86)\Microsoft Small Business\Business Contact Manager for Outlook 2010 Database Tool\ServerWizard.exe") add a new user for work with the Contact Manager under the built-in Administrator account - then there are no problems.
If you repeat under the account of the second admin2 admin, then "Database Sharing" - "Database Server Instance" (here it allows you to select a server), and in the selection field "empty. The user admin2 is in the list of users of the Business Contact Manager .
You need to delegate the ability to add users to work with Business Contact Manager to the second domain administrator under his admin2 account.
As I understand it, the problem arose due to the fact that when installing MS SQLExpress 2008 R2 during the configuration of the Database Engine, where the authentication mode was specified (either Windows authentication mode or Mixed mode), only the current Administrator user was probably specified. How to check it?
If this is the case, then how to correctly and painlessly add another second admin?
I assume that this can be done by means"SQL Server Management Studio" , but I would like to act not at random with a live database.