PC

A Pc is a excellent platform for multi media.
In case of audio, you don't need much power for play back.

There are many different strategies to obtain best sound quality.

You can choose between a sound card or a outboard DAC

 

Probably the PC is located close to your audio. Silent operation is required.

Laptop or desktop

In general laptops make less noise but there are exceptions to this rule.
You lack the space to add a soundcard of your choice to a laptop.
You probably have to go for a outboard DAC if you want to improve on sound quality.

Storage

HD's in laptops are 2.5”,quiet but limited in capacity compared with the 3.5” models.
SSD (Solid State Disk) is the ideal choice, no moving parts at all but 1Tb in SSD is a bit expensive. OS on the SSD, music on a HD (if on a NAS, you don't have to worry about noise) might be a affordable solution.

HTPC

There are Home Theatre PCs build with silence in mind.
Fanless PSU (power supply), heat sinks to cool the processor, silent kits for HD's, etc.

Performance

For play back you don't need much power. Any MP3 player or cellular phone proves this point. There are claims that it is even better to go for low power.

Less electrical noise is generated and this might be beneficial for the sound quality.

 

fit-PC2 Win7 Pro $499 1.6 GHz, 1GB RAM, 160GB HDD, WiFi, Windows 7 Professional
Marvell SheevaPlug $99 ARM-based 1.2GHz Sheeva embedded processor, 512MB of DDR2 memory, 512MB of flash storage, gigabit ethernet and USB 2.0. Big enough to run SqueezeCenter. See Sheevaplug SBS Server for dummies
VortexBox 500GB Micro NAS $399 Draws only 6 watts of power when fully on. Costs about $5 a year to run all the time. Automatically rip CDs using external USB DVD (Not Included). Automatically tags all files from online music database. Automatically downloads the cover art. Automatic sharing of file to SMB (Microsoft) file shares. Sqeezebox Server pre-loaded for use with Logitech SqueezeBox media players. Automatic reindexing of Squeezebox Server after every CD is ripped. AppleTalk - for OSX or Bonjour for Windows. DAAP - Automatically shares all MP3s for streaming to iTunes and Roku Soundbridge. NFS - For Linux boxes and almost anything else, Solaris etc. Easy installation of mplayer for AlianBBC support. Works well as a backend server for XBMC (XBOX Media Center) running on XBOX, Widnows, OSX, AppleTV, or Linux. Good support for Sonos music players. Auto select 120v or 240v power. Works in any country.

 

More on low power PC.

Parts

You can get all kind of parts to reduce noise level.

Big, low speed fans make less noise.

 

CPU cooler	HD silencer