Please help!

I have checked the box in the 2820 to use Wired Lan (PPPoE Pass Through)

And in the WAN setup on the 3300v, set the PPPoE/PPTP section with the adsl username, password and authentication settings etc.

However, Its still not connecting.

Is there anything else I am missing in the setup of the 2820?

I know its recommended to be used with the 120s, but didnt want to have to go and replace all the 2820s with 120s if I didnt have to.

Any help greatly appreciated... cheers!

In the WAN settings, try enabling Bridge Mode.
That should make it act like a modem.

Thanks, turned out I needed to change either the mac code on the 3300v wan setting or similar on the 2820 so that they matched.

Then worked.

Guessing also once the 2820 is working as a modem the firewalls and NATs cease to operate on the 2820 and it is then handled all on the 3300?