The rbr50 router in the rbk50 kit is a router only and cannot be configured as an extender, you could use it as a separate AP and you would the two separate mesh systems running. This maybe problematic if you don’t set manual channel as far away as possible. You could bridge the cbk40 system and use the 40 series as a modem only the connect up the rbk50 as your main router and mesh system as an option.
