It's fairly unlikely that IPV6 capable firmware will appear for the ST546 as it is an old model now. If you want to hang on to it and its current firmware while still having access to IPV6 you may be interested in this post:

http://forums.thinkbroadband.com/dslrouter/t/3962468...

I have done as described in the post as my existing ST585v6 is better than anything else I have tried on my lengthy phone line. I now have a RB750 behind it providing IPV6 connectivity to my LAN (currently via a tunnel broker),

In reply to a post by AdamF:

It's fairly unlikely that IPV6 capable firmware will appear for the ST546 as it is an old model now. If you want to hang on to it and its current firmware while still having access to IPV6 you may be interested in this post:

http://forums.thinkbroadband.com/dslrouter/t/3962468...

I have done as described in the post as my existing ST585v6 is better than anything else I have tried on my lengthy phone line. I now have a RB750 behind it providing IPV6 connectivity to my LAN (currently via a tunnel broker),

Thanks Adam that could be a solution to my problem as I have two ST546 routers and they can be adjusted to get 8128 out of my line. If I'm stuck with native IPV6 this could provide a workaround until I get 24 meg enabled at my exchange.

Note though that your ISP will need to support PPPoE for this to work effectively. I am currently on O2 LLU which uses RFC 1483 rather than PPPoA/E, which made the setup fairly straightforward in my case.

Another minor caveat - the configuration works well with a tunnel broker currently, but there may be issues when your ISP starts to provide you with a IPV6 subnet directly. The RB750 does not yet have support for DHCPv6 prefix delegation, although I think it may be coming soon. Depends on when and if your ISP is planning to make use of this as part of its IPV6 rollout (no idea what O2 are planning yet).

Caveats noted Adam. Will have to do some research and try and get my head round this as it comes online. Zen are also a bit secretive about their plans so maybe wait and see.