You should using CUBE to interconnect two PBX it is not safe to NAT a public IP to your CUCM.You will also need to using SIP Profile to modify the sip header so the calls can be returned to your public IP.

Just add the on the CUBE under global config.voice service voipsipaudio forcedOr you can go outbound dial-peer and add "voice-class sip audio forced"

Upgrade to 11.6.1 ES04

The command are in UCCX16.2ES02 readme for uccx user.Or Finesse 16.1 ES04 Readme for Finesse standalone user.  

I have read all of Cisco Caveated and found if you need TAC support, you can only deploy 1000 ova that is for BE6K.As VMware Cloud is running on 2.3 GHz CPU.