I guess maybe it might depend on how your lan is set up. I finally decided to set mine up like this:
rtp300 - xpbox - di604 - lan
and it appears to work well with ipv6, I do have some unrelated ipv4 issues (mostly vpn from the lan) I also had to enable the xpbox as an ipv4 router and add a route to the rtp300s routing table for the lan.
Here is the script I run on the xpbox (the lan xp boxes only need ipv6 installed, everything else is automagic)
rem This sets up the tunnel
netsh interface ipv6 add route ::/0 "Automatic Tunneling Pseudo-Interface" nexthop=::184.108.40.206 publish=yes
netsh interface ipv6 add address "Automatic Tunneling Pseudo-Interface" 2001:470:f:391::2
rem This adds the routed /64 to the network
netsh interface ipv6 add route 2001:470:g:391::/64 "Local Area Connection 2" publish=yes
netsh interface ipv6 set interface "Local Area Connection 2" forwarding=enabled advertise=enabled
netsh interface ipv6 set interface "Automatic Tunneling Pseudo-Interface" forwarding=enabled
"Local Area Connection 2" being my lan facing NIC, the rtp300 is my router, and the di604 is functioning as a simple switch. Hope this helps somewhat... took me quite a while to figure this out and I can't guarantee this is the absolute correct way to do this, but it works well for me.