I propped up a Windows 8.1 Enterprise machine and I want to activate it through my KMS server. I believe I have the relevant update applied (KB2885698) but I'm having trouble finding the correct host ...

OK, I've got a 2008 standard box (not R2) with a KMS host key installed and activated. "slmgr /dli" on the server reports that it is using our VOLUME_KMS_B KMS key. It's activated, happy, good to go.