this is very advances but a nice project!
snapfifo tmp is here:
/mnt/user/appdata/mopidy/tmp/
it is mounted to Mopidy /tmp/snapfifo and to snapserver /data/
all you have to do is to create another snapfifo pipe for the other Mopidy.
You have to change this locations:
Snapserver:
Post Arguments: snapserver -s pipe:///data/snapfifo?name=Example&sampleformat=44100:16:2
Mopidy3
[audio]
output = audioresample ! audio/x-raw,rate=48000,channels=2,format=S16LE ! audioconvert ! wavenc ! filesink location=/tmp/snapfifo