How to add EUS channel as a Base Channel in Satellite 5.6?

I added EUS channels 5.9.z and 6.3.z to my Satellite 5.6 system by running:

satellite-sync -c rhel-x86_64-server-5.9.z
satellite-sync -c rhel-x86_64-server-6.3.z

I can see these channels in my Organization, but they don't appear as a base channel when I try to change an existing server's subscription. I'm trying to move a RHEL 5.8 system to 5.9.z. It's been a while since I've added a channel. What am I forgetting?

Thanks