My problem is that Md's are assigned to rooms not EA's. You also specify which EA's each MD can serve, which is no problem, but the MD still needs to be assigned to some room when it is created, and each Room can only have 1 MD assigned it seems...
Ahh I think I get it now... the EAs are for having more than 1 "source" of media in a room, not more than 1 MD. There can still only be 1 MD in the room, and it can be a single "source" as well (ie playing back media files.) But you could, for instance, have a BluRay player and a STB connected to a TV as well - thus 3 sources, 1 BD, 1 STB and the MD.. the EAs allow the single MD to control 3 separate sources at the same time rather than the sources be exclusive - ie when the MD is controlling the STB to playback TV and you hit a media file on the MD, the MD doesn't automatically kill the STB playing back as it would normally, it allows both to play. Of course, as the MD is a single source, attempting to start some new media on it, will kill any existing media it is playing as it is in the same EA (as it should)...
This makes me think that it would be nice if the EA concept could be extended to allow an MD to become more than a single source... this could be used by adding multiple video and sound cards to the MD to control separate EAs, with separate amps and displays... also this could play into a feature request a put up ages ago, of breaking the "nexus" between audio and video. So that you could say play the audio from this media and video from that on the same MD, so that you can start visuals from one media file and the audio from another without one cutting off the other, or perhaps even merging the audio from both and the video from one (eg play a playlist over some background visuals - no other media player I am aware of can do this)