Question about Teufel Cinebar 11

Hey everyone
Als you know the Teufel Cinebar 11 ist available as 2.1 (Bar + Sub) and 4.1 (Bar + Sub + Rear) System.

And If i understood it correctly you can retrofitt the 2.1 System with two Rearspeakers.
But i did not find any information about what Rearspeakers i need.
Do i need the Teufel rears because the system does not accept any others or can i use "any" Bluetooth speaker ?

Thanks a lot