Hi,
did you get this resolved?
We are in the same/similar boat as you.
We have MAK and KMS keys for 2012 Datacenter but only KMS for 2012 Standard.
I spoke with Microsoft Volume Licensing and they said that with Windows Server 2012 Datacenter, They said that Iinstallation of Windows Server 2012 Standard can only be as a TRIAL, however, any lower version is fine (e.g. 2008, 2003).
I have seen two documents that seem to suggest different things.
1. One document that says that I can install the same EDITION (being Datacenter) and any lower year (e.g. 2008)
and
2. One document that shows a Virtual environment with 2012 Datacenter as the Host and then Windows 2012 Standard, Windows 2008 Standard, etc. as virtual guests.
cheers,
itatcapital