Asterisk and Cisco phones via IPv6

The last few days I am trying to register some CISCO phones (7911, 7961, 7970 all with SIP firmware) to Asterisk (v11) via IPv6 only (without dual stack) unfortunately without results…
Can someone please to share experiences with this kind of configuration?
I’m not sure which entries should be placed in the SEPxxxxxxxxxx.cnf.xml

I will be grateful for any help,