Well, looks like I've tried everything I can, so I can only conclude that either the wireless on the remote doesn't work (seems unlikely as it can see the SSID), or it just doesn't like my router for some reason.

I'm really not sure what to do now. The WiFi was really the only reason I chose the RC9800i which now looks to have been a poor choice. I suppose I'll just have to see if I can return it and try something else...

Paul