There are many linux distributions for audio which don't require a separate server like the Squeezebox model. Volumio is one that is very easy to install and use. Voyage MPD, Audiophile Linux, Deadbeef, HiFiBerry, Raspbian, RuneAudio and many more. These all run on "embedded hosts" which means tiny, inexpensive computer.
There are also daughterboards (called "capes") which expand the functionality of the host. For Raspberry Pi there are DAC boards that plug into the host to make a complete, self contained unit with file server/library management, client player/network remote control, and I2S DAC. It's like a DIY Sonos with better construction and sound quality than Sonos and the freedom to customize apps, filters or whatever, for about half the price of Sonos. Expandable and changable whenever a new OS, host or cape comes out.
IQ AUdio, or
RPi-DACI like the driving to the park analogy Mike. Most SB users have had their fair share of struggle over the years, often with no good fix available. There are solutions to every imaginable issue in the linux world and many friendly people committed to growing the linux community who are happy to help. With hardware cheaper than dirt it is starting to bloom now. I think Linux will go mainstream in a couple years when people get tired of Microsoft and Apple crap and when a visionary can market Linux to the normal, non-geek youths. If someone made a linux OS that ran on iphone that could ignite it if they could penetrate the media defense of status quo.