If I'm not mistaken (FWIW, I haven't seen many of these types of B&O devices), it has some sort of proprietary centralized connection module, not completely unlike what Bose uses. So in this regard, you would likely not be able to simply add on two more speakers to gain 7.1 sound.
Why not contact Beolab support directly since it directly involves configuration of their product line? You could also ask at AVS forums if they did not respond.
I am planning to purchase Yamaha RX-A3030 and Beolab 14. Since Beolab 14 is only 5.1, I want to connect the speakers and subwoofer directly to the Yamaha receiver and purchase 2 additional Beolab 4000 and connect them to the 2 pre-outs on the Yamaha.
Can i use combination of speaker output and pre-output to get the 7.1?
Thanks in advance