Over to you?
I can only think of two test points.
One would be trying both wired. If the sb is wireless, try (for testing) a wired connection and see if it goes.
The other would be to get a new nightly at http://nightlies.mt-daapd.org and installing it. Go into the plugins folder (c:program filesfirefly media serverplugins) and delete (or move) the daap.dll.
Then start it as normal and see what that does. If it says “no libraries found”, then it doesn’t see the rsp for some reason (router?). If it sees the library, then something strange with the sb.