Last update about the Audio-amplifier project,
While i was messing around to build a testing NAS with a Pentium D based set up (irrelevant to be used as a 24/7 NAS due to high power consumption of the platform...), i found an old 12Vcc/2.5A PSU from a broken external USB/Firewire HP DVD writer (that i had forgotten to own >_<).
The wires were slightly damaged, so i simply re-soldered to the cable i previously made.
Here is the final result :
The Audio-amplifier project is now Closed and considered as finished. It is neither slick nor compact, but it's mine and works pretty well!