Using a 2860ac with firmware 3.8.4.3 (and previous versions) I am unable to get IPv6 to work when using WAN2.
Due to line length and stability issues I am currently having to use an external modem on WAN2 - exchange is an ADSLMax and I am at about the distance limit for ADSL.
IPv6 does work when using WAN1, however the line stability is such that DRM limits the speed to an unusable level.

WAN IPv6 is set to PPP, LAN IPv6 is set to use WAN2 as primary interface - in fact all the settings (except Primary WAN Interface are set the same as when I am using WAN1)

I have tried two different modems (Vigor 120v2 and D-link DSL-320B) without success. Draytek support are of the opinion that it should work.

Any ideas anyone?

Now using a Zyxel AMG1202-T10B in bridge mode - again without success. Is anyone using WAN2 with IPv6 successfully?

my current understanding is that currently without a lot of hassle and a fixed ipv6 address/space plus NPT v6 there is no way to have multi-wan and IPv6. There seem to be proprietary solutions out there with tunneling but nothing for the home/soho usage. If you find a solution I would be VERY interested