IPv6 Settings

[BillS]

I am trying to setup IPv6 on my RT-N66U running Shibby Tomato Firmware 1.28.0000 MIPSR2-140 K26 USB AIO-64K. From my ISP I get Delegated Prefix and IPv6 Gateway Address but my routers firmware only has a box to fill in Assigned / Routed Prefix in the Native IPv6 from ISP Service Type and only boxes for DNS servers in the DHCP with Prefix Delegation Service Type. I am in Brazil and using .Net cable as a provider and they don't seem to be able to give me any help so it has become trial and error on my side. I am sure one of the ISP Service types works but which one. Having said that I have tried the Native IPv6 from ISP and filled in the DNS servers but that has not worked so it leaves me with Native IPv6 from ISP but I don't know what to but in the Assigned / Routed Prefix box. Is it the Delegated Prefix address I get from the ISP or the IPv6 Gateway address?
The reason I am able to see the Delegated Prefix and IPv6 Gateway Address is because I have their Modem/Router/Wi-Fi/Telephone device setup in Bridge mode but prior to setting to Bridge I viewed all of the settings and wrote them down then switched to Bridge mode.
Can anyone tell me which of the two I can use to get my IPv6 working?
Thanks

[Philip]

I would use the Delegated Prefix address you got from your ISP as the "Assigned/Routed Prefix".

Some ISPs have buggy IPv6 implementations initially, especially if they don't know how to advise you to set it up.

[TonyT]

No real need to use IP6 yet.