prefix delegation size with SB8200?
I recently gave up my static IP addresses and figured I'd switch out my comcast provided modem with one I own. I purchased an Arris SB8200. Once provisioned, my CPE requested a prefix delegation (configuration unchanged). I received the same v4 address but only a single /64 for v6, which is insufficient since I run more than one VLAN. Comcast was unable to provide me any assistance as they said they can't see any configuration in that modem. The web interface provides no tunable options and very limited visibility into anything but the log and the HFC channels. Docs for the Arris aren't terribly helpful.
Long story short, I switched it back to the comcast gear and will be receiving a new device from comcast to address my v6 issue. My question is this:
Are there any folks out there running a business connection on a SB8200 and getting more than a /64 of v6 space? If so, how?