Your CMTS is ready for IPv6. Please check this website for modem support. - See more at: http://mydeviceinfo.comcast.net/?s=i&so=1&e=0&d2=0&d3=0&tier=-1&sc=570
My modem is a self-supplied SB6121, which that link says supports IPv6.
What else do I need to do to get IPv6?
You need a router that supports DHCPv6 w/PD.. What type of router do you have?