Headphone/Speaker Amp

[magruder13]

I am planning on moding a ps3 slim and a gateway monitor just like ben did. I am very new to modding and making computer components. What I am trying to do is use the PS3 PSU to power an amp that will control volume (by the turning of a nob) and either play though a headphone port or speakers. I want the speakers to be as loud as possible but my input is only 5V and 3A.

I know how to solder and do all of the physical making of this component (is that even what it's called?) I just have no idea how to design it it or even if is electrically possible.

Thanks,

Magruder