Ok, it's still not 100% working, but at least I've got a "work-around". See, Trio won't go through my Linksys Gigabit Switch!!! SImple test - hook each Rio up to the router directly, hook the server up to the router - works (even in multicast) - listen mode works, too.
Now, pull the server, plug into the Gigabit switch, and no workie. Nunca, nada, zip.
So, I can either pop a 10/100 card into my server, or is this some kind of clue as to something else to try?
-Dan
PS: Using the Java front-end is really nice for adding songs to the queue of the "listened-to" Rio. COOL!