Small system. Low power is the key

I got an celeron 2,5 ghz system i use for playing music and just that.
My plans are to make the new system handle dl(torrent) and playing music and always be on.
I want a pico psu 60-80 watt.
1 harddrive 500-1000gb (this i got).
Atom or something like that, with no fan. Spdif output for stereo sound.

Key is silent and low power. Goal is around 20 watt for the system. Max 30 watt. But lower is better.

Is it possible??

Budget for the cpu/motherboard is around 150-180$