Hi,

the SBS 2011 environment is a VM on a Hyper-V 2012R2 server

I need to add a Server 2012 R2 Essentials  to this as host for the Hyper-V replica and also serve as Backup domain controller ..

How do I proceed ...?

Many thanks

You want to add a Second VM onto this machine, to be a backup domain controller?

That is a simple VM, easy to add. (DC2)

Then you can add a second Hyper V Host (physical machine), to be the replica host (HV2)

So, HV1 will have a active copy of Essentials, and the replica of DC2.

HV2 can have the replica of Essentials and the Active DC2.