The BM5500 can drive two sets of speakers (actually more) from the two pairs of speaker outlets. Both outlets (pairs) will take the 2 pin DIN plugs to drive two pairs of passive speakers or two pairs of Beolab Penta or both active and passive (pairs of) speakers.
If you connect a 4 pin DIN type plug to speaker 1 outlet Speakerlink you can drive Beolab Penta 1,2,3 and get the display data on the Beolabs. If you connect a passive speaker, e.g. Beovox Penta to speaker 2 then both pairs of speakers will be driven as well. Mute will only work on the main speaker 1 pair.
If you connect a 3 pin DIN type plug to speaker 2 outlet you can connect via an XTra speaker box a remote pair of passive speakers (or even a chain of XTra boxes). The datalink information goes down the 3rd wire so you can connect Beolab Pentas to the XTra box and get data display on the main Beolab Pentas and the remote ones.
For you, I would suggest making up the 4 pin DIN cable (difficult to buy and you will have to source or “manufacture” the four 4 pin DIN plugs). Beolab Pentas will be driven by the amp in the speaker – very little output comes from the BM5500. If passive speakers are connected, they are driven by the BM5500 and will need higher current cable.
Have a good read of “Beolink Master Control Handbook”. Try not to get too excited about the capability of running 2 sets of speaker in different rooms. I have a BM5500 with Beolab Penta 2 out of speaker 1 and an Xtra box driving Beovox Pentas out of speaker 2.
For cables, you can always try Steve at Sounds Heavenly but the 4 pin and 3 pin DIN plugs (made for B&O) are almost impossible to obtain (although I have been lucky on ebay once in a while).