Each powerlink socket can handle up to about 10 speakers connected at any given time. This is not to say that anything close to that would be a recommendation, but it's feasible.
Connecting 4 speakers to an audio system does not actually decode different information for rear channels, but simply replicates the front left and right (like in a car). If you wanted to take advantage of true multichannel audio, this is not doable with only the items you've mentioned.
As for the final result, everyone else put your two cents in, but if I were to do this I would want my front and rears to be identical so that their "voices" matched. Since the info will be identical in the front and rear.
Also remember that the BeoCenter 2 only has one PL out like an active kit, so you'll need a few Y adaptors.
Cheers!
There is scarcely anything in this world that some man cannot make a little worse and sell a little more cheaply. The person who buys on price alone is this man's lawful prey. - John Ruskin