Has the CX8091 allready been released?
You can install the Beckhoff OPC-UA Server on every CX that has enough Diskspace (which the CX8000s has, I guess). I have tested OPC UA Server on a CX9001 and its pretty easy to use.
Just follow the guide here: http://infosys.beckhoff.com/english....w.htm&id=28677
I don't know if the CX8091 comes with the OPC-UA Server allready installed, but you can allways buy it sperately.