avast! NetServer 4.8.1061 is compatible with MS Windows Server 2008 x64 R2.
We have some customers working with this configuration.
In two customers, AMS Server is a MS Windows Server 2008 x64 R2 and they are using avast! NetServer 4.8.1061 to protect the servers. In both cases the AMS server is managing more that 1500 NetClients and NetServers.