The amplifier is based on 2x2 LM380N-8 that gave a pretty sound on the first tests. Stereo circuit is also doing well, look at the scheme attached to see how I built the whole thing.
It needs a 12V voltage supply and give back a 2.5W output power. I linked the amplifier to two Visaton speakers (FRWS 5 SC). I soldered everything on a prototyping plate which makes everything look cleaner. The sound got better too.
I have received the Bluetooth module I order on ebay. After some hesitations about how it's working, I've added it to the circuit and it works! I still got some noises, I'll try to fix it with some capacitors at the input.
Details also available here. The bluetooth module needs a 3 - 5V battery. For the moment, I am only an external battery, I'll have to look for a solution to integrate it in the circuit.