Why port 6699? Your DI-604 is a linksys isn't it? Is it a modem or a router or both. From what I could find it's just a router which suggests you have a separate modem.

Anyway, whichever port you choose (LW is set to use port 6346) you will have to set LW to use the same port or vice versa. You will also need to Force IP. See Force IP instructions & sample image And also set theat same port number under LW's port option (see Tools>Options>Advanced> & both Port & Firewall

See how you go.