First of all, firefly does not support uPnP.
It uses the RSP and DAAP protocol.
As Pinnacle is not licensed to use DAAP, the soundbridge only supports RSP.
But as protocols are implemented, you won’t notice the difference.
Firefly broadcasts itself over the network. When using a wireless router, multicast/unicast must be enabled for this to work. Check for that option on your router first.
Also, the router model sounds familiar. Do a search on it on the forum, it might give some handy results.