Für alle, die an einer Lösung für eine KMS Aktivierung von Windows 10 mit einem Server 2012 R2 interessiert sind.

• In VLSC - click License, then Relationship Summary.
• Now click the License ID of your current Active license.
• Once the page changes, click Product Keys.
• Scroll down the list and look for "Windows Srv 2012R2 DataCtr/Std KMS for Windows 10". Use this key.

Requirements:

• Windows Server 2012R2 with Volume Activation role installed
• KB3058168 Installed.
• Currently does not work with 2008/2008R2. I'll look back through my history, and once I find the link about this, I'll update.

Trying to use the key listed under Windows 10 (whatever edition), will result in an error message. Basically because you cannot use a client KMS key on a Server. Since the key listed there would be a client key, we have to use this special one until Server 2016 is released.

Quelle: http://www.reddit.com/r/sysadmin/comments/3fh9gv/steps_for_windows_10_kms_activation_against_2012r2/