MR816x outputs 3&4, 5&6, 7&8 not working?

I am trying to set up some external processors with an MR816x and cubase 5. I have been able to do this in the past but now I can’t get any levels sent from the MR816x to the processors.
Outputs 1&2 work but if I change the outputs in connections and move the leads to the other outputs…nothing??
I am lost with what to do now, can anybody help please?

It seems like they cannot be controlled within Cubase, they have to be turned up in the MR editor first??