BOY!
I'm having problems too.
I have an older Mac Pro running Lion (10.7.5) and am trying to use the Ethernet connection to sync with a new Mac Pro running 10.12.5.
After I set up different networks in Audio Midi Setup utility and click connect I can an error message on Sierra saying that that the IPv6 connection was refused (by the Lion machine).
I have tried every conceivable combination of DHCP, manual etc. One online resource said to disable IPv6 in the Sierra machine. nothing happens. When I open SystemPreferences/Network window on the Lion machine it says there is a connection via the ethernet port (green dot). When I open SystemPreferences/Network window in the Sierra machine the Ethernet port says: "self-assigned IP address" regardless of how the network is configured.
It appears after many hours with Apple Care on the phone (they were essentially useless) that Lion is not spitting back a IPv6 ping to the Sierra machine resulting in the error message. It appears that VEpro will not work as I can't disable IPv6 in either mac.
HELP!!!!!!!