Two sites with a BE 2012 appliance at each site

We have two sites and a BackupExec 2012 appliance at each site. We backup servers locally at each site a duplicate the backups to the respective remote site. We do this so that if one of the appliances is unavailable the other can be used to restore backups. Currently one of the appliances is CASO and one is MMS, but if we have to change that we can.

Unfortunately when I tested the CASO being unavailable the MMS could not be used, the services just don't start on it. I've been advised that we cannot have two appliances that will work independently of each other in the event of one being unavailable, and duplicate between them when both are available. Does that seem correct?

Is there something that we can do to meet our requirements?

Thanks