I think if you bought an Eos with the RCD 300/310 then you only get the 4 speakers in the front. When you get the RCD 500/510 then you get 6 speakers - 2 in the back.
The next upgrade is DynAudio which adds an extra 2 speakers in the back.
The next upgrade is DynAudio which adds an extra 2 speakers in the back.