I am testing multi-zone and.....
Just an observation/theory. I have a full two zones in the car and the 3rd should be complete this summer. I am playing with / testing version 0.9
I have noticed (and possibly mentioned in the forum elsewhere a while ago) that there are some issues with assigning inputs to zones.
I just started browsing the SVN sources so cannot validate my "theory" yet, however...
I think that input device naming may be the issue. I noticed that, in the zone settings screen, if there is more than one identical input device name it only shows once in the list. My thought is that somehow identical text names are being condensed such that only unique names are used. It might explain why I notice issues with assigning devices.
This issue may carry on to audio zones as well. I had added two identical USB headsets which generate identical device text descriptions and had issue trying to set them up as different zones. Enough issue that I could not do it successfully. I resorted to buying another different headset and could see two different zones.
These are just observations. And my "thinking" may be out-of-whack, it's just based on other coding experience.