Hi
From the problem description I understand that you have the new and old server integrated with the same CUCM cluster, is that correct ?
If yes I am curious to know how you will be migrating users from time to time.
The best and the easiest way will be backup the old UCCX system , install the new server with the same hostname and IP and perform a restore, the resotre process will automatically integrate UCCX to CUCM, and migrate all the data to the new boxes
Thanks
Anuj