Most likely you will want to wire them in series, depending on the impedance. The diagram you posted shows two series pairs wired in parallel. Assuming the same impedance for all the drivers, this method would get 4 drivers to the same impedance as the drivers individually. Remove the two driver on the right of your diagram and you will have two drivers in series. That will effectively double the impedance of the individual drivers.
Most likely you will want to wire them in series, depending on the impedance. The diagram you posted shows two series pairs wired in parallel. Assuming the same impedance for all the drivers, this method would get 4 drivers to the same impedance as the drivers individually. Remove the two driver on the right of your diagram and you will have two drivers in series. That will effectively double the impedance of the individual drivers.