Hi
had an answer from Draytek themselves on this one.
The 2800 only supports one local subnet. The 2nd Subnet is for IP routing usage. This allows you to use the second subnet to divert PUBLIC IP addresses to devices behind the router and bypass NAT.
Unfortunately no amount of tinkering will allow you to use the second subnet on the router in the way that you desire.

The 2830 series of router DOES support multiple local subnets, up to 4 in fact. So this would most likely resolve your problem. Its the modern day version of the 2800 with a whole host of new features added.

Thanks for the help and suggestions and I hope this answer will help anyone else looking for the same solution