http://www.sophos.com/en-us/medialibrary/PDFs/documentation/utm9200_manual_eng.pdf
6.5 IPv6
"Starting with version 8, Sophos UTM supports IPv6, the successor of IPv4." Seems out of place in the version 9 documentation (carried over from v8 docs).
6.5.5 Tunnel Broker
No mention of Hurricane Electric.