Thanks pop80_uk. Port what MAC address though? The CM already reliably connects with the NICs of both my desktop and laptop. It seems it only has issues with the MAC of the Router's WAN port. Assuming the MAC is the problem...
I'm going to initate the return of the router anyway, but I can't escape the feeling that the problem will remain. I can just hear the TW support now, "We don't support router's....." Which is a handy policy to have, 'cos it means they can ignore you when you have a router in your system.