A sylink.xml replacement on a client will make the client communicate with the management server. You need to replace this file on every computer that needs to be connected to SEPM.

As far as GUP is concerned, you need to specify in the management console's policies, which computer will be acting as a GUP. That computer can provide virus definitions to the computers in the same group.

If you want to see all the clients in a group, and if those clients are not in the management server, then you can replace the sylink.xml file on all of them. Once they all show up in SEPM, you can make one of those computer a GUP.

Let me know if you have more questions.

Cheers,
Aniket