As you guessed! 2WIRE kindly advised that:
To get the necessary firmware update you will need to contact BT directly. They should be able to publish the firmware update to your gateway.
When I told them that I am not with BT anymore (and with their Phorm shenanigans it's unlikely I would want to go back!) they responded:
The ISPs have complete control of distributing the firmware to their 2WIRE models.
So much for that. I don't know if the ADSL2+ technology is a hardware, or a firmware implementation issue. I guess if the chipset is too basic it may not have the necessary instructions to perform the programmatic functions required to process the ADSL2+ signal.
All this quest started in the hope of finding a modem that will hold the signal at my relatively long/noisy line better than my DG834 can do. I have read that some people had success with the Thomson Speedtouch (
http://www.hmmm.ip3.co.uk/adsl-snr/) and others with the billion bipac routers (
http://forum.kitz.co.uk/index.php?topic=1875.0). I don't need to reduce my noise margin (it's already set at 6dB with an attenuation of 39dB & a sync speed of 6976 kbps) but I am hopping to find a device which will hold the sync speed above 7392 kbps so that I can notch up my IP Profile to 6500. Meanwhile, I thought that getting the best sync speed and SNR stability was a matter of matching your router chipset with the BT exchange chipset. My local exchange DSLAM currently has a STMicro Alcatel chipset but I have no idea which routers work best with these.