Don't try to stream to an Apple's Airport Express device through a router.

For years know I stream my music to my stereo using Apple's fabulous gadget: Airport Express. I plug it to my stereo, open my laptop, launch Itunes and bam! I know can start listening to music in my stereo. I remember vaguely (like we all do) how I set up the device years ago(5 or so). One thing always intrigued me. Why iTunes running wireless see the service but iTunes running on over Ethernet on my Mac mini sees nothing. When I launched Airport Setup Utility and hit scan, it finds nothing so I have to hit "other" and punch the IP of the device. Then it finds it. Why the scanner doesn't work? I never minded the issue since my laptop worked fine so I have no need to stream over the wire. That changed last week when my company reduced ranks and took a way my laptop (yeah, their laptop) and found myself unable to play my tunes over the Ethernet. After poking around the Net I found no good leads that resembled the problem. I can ping the damn device. I can set up static or DHCP for the device. It works every time but ...the big but ... the utility scanner doesn't detect and iTunes says "nothing here, move along". Short from opening wireshark and start sniffing packets I went ahead and removed the Airport Express from the Linksys router BEFSR41 and plug to my baby switch Linksys EXXS55W (an itty bity workgroup switch) Bam! The Airport setup app instantly detected the device and iTunes popped the option to connect to it. Meaning. The streaming is not an IP based protocol? That would be my conjecture. Short to go on the web and find out the nuts and bolts of the protocol I just made a memo to self: Memo to self: When using an Airport Express device and there is a need to stream to it over Ethernet: DON'T PUT THE DAMN THING BEHIND A ROUTER, IT WON'T WORK. Enough said.