When XSAN clients are connected to a Stornext FSM (mac_fs in this case) you can query the client version as such:

[root@cx-node1 mac_fs]# cvadmin -e "select mac_fs;who long" | grep Darwin
 Revision  : 4.7.2 build 564[46152] for Darwin 15.0.0 x86_64
 

The Darwin version (15.0.0) correlates to this table under the Version Column which can been seen in its entirty here: https://en.wikipedia.org/wiki/Darwin_(operating_system)

This gives you the OS X Version (v10.11.0).  Next you can reference the latest Stornext compapiblity guide here:

http://downloads.quantum.com/StorNext5/5.4.0.1/6-68043-01_RevAF_StorNext_5_Compatibility_Guide.pdf

Providing the most recent XSAN client versions here for reference: