OK, as a last try, I decided to get my old Dlink 802.11b Access Point out of the cupboard.
This baby is 7 years old!
Configured, plugged into the network, reconfigured the SB to use that Access Point, and voila!
tcpdump shows a very different picture with the server (Firefly) talking to the SB from port 3869 and the SB talking to the server with port 5353.
Who would have guessed a 7 year old Access Point would work better than 3 year old Wireless Router?
Thanks to all who suggested things. Hopefully,this info will help some other poor soul.