OK, it turns out my provider in the states does offer a 6RD connection, I got it running last night using Opendns for domain name resolution.
Mine gave me trouble doing a manual setup complaining about addreses but when I used the built in wizard it took the same info and worked great. This was with a Dir-825, not a 815.
But my address conversion and everything is seamless.
Are you running the latest EU firmware. My understanding regardless of the IPV6 address the router should handle it, mine did. The firmware is fluid for IPV6 and until more people use it, it will not get debugged.
Furry, you may want to PM him a way to escalate the problem.
Just looking, my 6rd connection is /32, but once is configured itself, /64 and /128 seem to be prevalent in the router.