I thought the modem was the problem originally. Then I found the IGMP snooping switch and the service finally appeared. It doesn’t add up though that the router is still the problem. The firefly service on the LS (wired) is getting through the router to the PC (a wireless laptop) running Bonjour, and the mDNS packets are also getting through the router from the PC to the soundbridges (wireless).
The uPnP switch is to open up the router itself to uPnP discovery, it is not a passthrough switch.
I know many others have solved their connection problems with new routers, but its not a certainty. I should probably upgrade the DLink firmware first before spending more money.
Thanks for the response.