MirrorView between CX4-120 and VNX5300 Unified

Hello at all, for a customer i will configure mirrorview/s between an cx4-120 and an vnx5300 unified array. First problem was the domain. i can´t add the vnx to the existing local domain. The warning said, that there is no support for vnx for block, file and unified. On the vnx runns 5.32 and on the cx4 release 30. Is there existing an documentation? Should i use multi domain? in the existing domain is also a second cx4-120 and one cx3. Between the two cx4 is mirrorview/s configured. First,the customer will migrating the LUN´s from the first cx4 to the vnx and then he will mirrorview between the vnx and the second cx4. What happens with the existing mirrorview connection, when chaning the domain? Thanks a lot. Karl