Zscalar is a virtualized VPN while XQ is virtualized software encryption.
Zscalar is a managed VPN to compete with Cisco. Though virtual, it is controlling and connecting access to the network, not protecting data at the data access level.
XQ uses zero-trust to protect the data itself, not the network access as in the case of Zscalar.
XQ additionally provides management of content only readable by people/apps/endpoints who are supposed to read it. The content itself is encrypted in a distributed data approach whereas Zscalar is not aware of who or how data is accessed after it arrives at the end destination.
Zscalar and XQ can work as complements of each other.