Well, I don't know what made it not work for you guys, but it never stopped working for me. Ever. From the first post, I understand that you have two flooplands, one for each floor? I never tested that. Looks like no one did, since you can select MDs from the hidden floorplans as well, through the selected floorplan (or so the reports I get say). If you have a single flooplan, it should work fine:
1. Select the MDs you want the media on -> they get listed in a comma separated list
2. Select the stream you want to play in the selected MDs
3. See it happen
When you do this, there's a "Move Media" message sent out. That one has a list with the selected MDs, and it end up in Xine, which processes it in a "Play Media" command or something. I don't know precisely.