Hmmm... the half-bridge option is one that Zoom suggested to me but only having one of 3 machines able to access the web is no use to me.

I wonder if I ultimately need to ditch my Zoom x3 for another modem that supports UPnP ?

Sadly I'm in the dark as to a) what that implies and b) whether most modems these days support it !

Have set up static IP address but my IP address hasnt changed in ages

Not sure how you put the LAN IP into the DMZ... modem's IP address is 10.0.0.2 - you mean put that into its own DMZ ? Will that work ?

Lnksys Router doesnt seem to have a DMZ section