Can I use Focus XD as a rear speaker?

Focus XD can be used effectively as a rear speaker if connected to the analogue pre-out outputs of the surround receiver to the analogue speaker inputs Analog Audio In.

Please also see the Focus XD manual page 19.

If using a Hub / Connect Focus XD can even be used wirelessly by connecting the Hub / Connect to the pre-out outputs of the surround receiver.

Theoretically, several Hub / Connect (set as A, B and C) can be connected to the front, center and rear outputs of the sound receiver, although the simultaneous use of multiple Hub / Connect can lead to sound dropouts, depending on the utilization of the wireless network and is therefore not recommended.