Thanks for your interest. Let me know where the best place to start putting pages would be and I'll get started. I plan on either writing a wrapper for mplayer, or if that is not feasible I'll write something from scratch using the mplayer library and the jack library. I envision having a device instance for each zone much like adding squeezeboxes. I think this is doable unless I'm missing something in my understanding of how things work in pluto. If I'm correct, my device will work with pluto's media infrastructure and just happen to run on the core rather than on a remote device (though in theory jacks architecture allows for that sort of thing). Setting up zones is simply a matter of assigning jack output channels to an arbitrary zone number/room. The back end would then connect the output of the mplayer plugin to whatever jack channels are assigned to where you want to here music, including being able to connect all channels to have the same thing playing throughout the house in sync. That's the plan.
Any help, ideas and or testing would be greatly appreciated.
I see that you're doing something similar that I also tried to. Also you're dealing with problems of distributing audio to several zones. That's exactly what my idea is also.
But I more think in a way to add Audio only functionality ot existing Xine player (since a lot of efforts will be put into its development).
AFAIK, Pluto guys (specially Kiril) are working on one to many sync and streaming feature of Xine Pluto wrapper, so I guess this is similar thing, except you do it with Jack (unfortunately I don't know it well - but have always thought about having one audio switcher/mixer for whole house audio implemented in SW and I think your work is pretty close to that).
I hope that I'll be able to work further with Kiril on this feature after 0.43 release.
But for both (me and you), problem of support for 3rd party media players is major pain - it's currently non existant and on lower priority on task lists. So maybe we can join our forces and try to do something useful....