Installed and restored library ok on El Capitan 10.11.6.
I did have a few issues:
1) The settings that I had for MC21 included running Media Network. That used to show a Media Server icon in the Menu Bar. I'm not seeing that now. Is that by design or indicative of something wrong? The DLNA server seems to work OK - I can receive from it on other devices.
2) Gizmo web control presents a completely blank page.
3) For a while, MC wouldn't shut down fully when I clicked on either File/Exit or "Media Centre 22"/Quit. The UI would go away, but a task remained running (visible with Activity Monitor). Restart wouldn't work until that task was killed. Normal quit did not suffice - it required a "force quit".
That remained a consistent behaviour for a number of start/stop cycles, then suddenly it fixed itself. I hadn't rebooted or anything, but I was fiddling with the server configuration - enabling and disabling DLNA while I verified the situation described in point 1 above. Seems fine now...
4) I'm getting lots of logged messages of the form: "Class XXX is implemented in both /Applications/Media Center 22.app/Contents/MacOS/Media Center 22 and /Applications/Media Center 22.app/Contents/MacOS/Plugins/YYY.dylib. One of the two will be used. Which one is undefined." Both XXX and YYY have lots of values. Looks like you've got the same set of ObjectiveC libraries in many files - presumably this will be refined as the code settles down?
Keep put the great work!!
Brian