Unfortunately you will need two independent AQM/Calabrio base servers per UCCX cluster integration. For that reason /limitation you cannot have “an extension” of a recording server to record agents from 2nd UCCX cluster.
Network recordings are based on CUCM integration and recording profiles. Depending on the number of recording servers, you will need to set up the same number of recording sip trunks accordingly. Then you update the phones to point to the correct sip profile… that are part of the one AQM base server to UCCX integration. You will only see the agents of that single UCCX integration only. To see the agents on the 2nd UCCX cluster, you will need 2nd AQM base server, and its associated recording servers, integrated with 2nd UCCX.