yesterday i added my sixxs account to the astaro. At the dashboard it shows state up but the link stays down. In the log it says that it successfully retrieved tunnel information.
Have you enabled prefix advertisements or dhcpv6 ? If not, have you set manualy the default ipv6 Gateway on you computer ?
A good test is to go to an ipv6 ready web site(www.sixxs.org) with the proxy enable on your browser. If your sixxs tunnel is good the "proxy" use an ipv6 adress and you can see it on the site.