I think I am working towards something similar to what you want to do:
1. I have a zoned Xantech system, and each zone is a room (living room, bed room, play room, etc). The eye in each room feeds back to the basement and emitters from the zone controller will send the output to common equipment or ones just for that zone (not using the latter yet).
2. My intent was to add global cache to be controlled by CQC. It could (via converters from gc to xantech) send commands to the equipment as well. I expected the equipment to be centrally located (or as much as possible, probably the living room and the basement aside from sage extenders in the rooms).
I think the piece behind your question is what are you expecting to share?
I use Sage for tv distribution throughout the house. I also have Sony DVD Jukeboxes that get modulated over coax and get pumped through a component video setup. Right now I just have the xantech, but I'd like to select movies off a touch panel (the intent being with cqc) and have it send the sommands over the xantech network to make it happen.
The complication, which may be where you are headed is how to tie in the local equipment with that type of command. For example, also changing the inputs on the local tv in the guest bedroom aside from powering on the dvd jukebox and selecting the right movie. In that case, I thought a gc100 in the local room with an emitter would do the trick, but I am not yet there. I had also tied with running an emitter from the xantech in the basement back up via a wall plate so it can send it directly. An IR sensor only uses three conductors and if cat 5 is used... This can get complicated as well (it has to go to the proper zone if you might have the same tv's for example in different rooms).
This was another reason why in my case I liked the possibility of using HD extenders for sage, tying in the jukeboxes as channels within sage (like collinr recommended), and tying in the elk/cqc within sage as well (ala IVB). It just solves so many problems and keeps things 'simpler' (insert comic relief here).
This happens to be tied to why I was dealing with moving my sage server to the basement (to get it connected to the jukeboxes).