Hi!
I literally swapped the rear speakers three weeks ago. I used this guide on the forum which guided me through the process
http://www.peugeotrczforum.co.uk/viewtopic.php?f=20&t=10771
I only changed the rear speakers to the JBL Car GTO 939, in my opinion the two front speakers who are producing high and medium frequencies are good enough. Please be warned, Peugeot did an excellent job at making the rear speakers as inaccessible as possible, changing them will take you 3-5h.
The rear speakers are connected by two small wires (standard red/black) but the connector is custom made by Peugeot and not reusable. I had to cut the wires and solder a new connector along with a cable extension to it. Furthermore, the plastic casing that holds the rear speakers in place is also custom and will most likely not fit your speakers. I had to cut the plastic casing deeper into the room behind the speakers (where the rear tire is), and screw the speakers onto a wooden ring which I then attached to the plastic case.
It looks like you have everything, two oval big speakers for the back, two medium speakers for the doors and two small speakers for the dashboard.
I don't have confirmation on this but the amplifier in the stock radio should do 25 watts on 2-4 ohm. The rear speaker I can confirm are 25w and made out of cardboard. The factory speaker are not bad, but they are also not good. I highly recommend changing the speakers, it makes a big difference.
Fun fact: The RCZ has virtually no sound dampening. My friends hear my music in their houses when I'm parking. Be prepared to have the world listen to your music while you drive on high volume.
I'll be glad to answer further questions, but I can only speak for the rear speakers, I did not bother to change the rest. The bass is gently massaging your back through the seats, windows are very slightly shaking but anything more than that and you're entering the realms of insanity. My friend has a 2k watt system in his van and I hate it, it's just compressed air and rattling from the car's plastic.