Take a look at the linksys NSLU2. Over at http://www.nslu2-linux.org they have easy step-by-steps on hacking it to run linux. A debonaras loaded slug will run mt-daapd well, as will one running unslung.
Unslung packages are on the nightly feeds.
That’s what I use to feed my soundbridge — a nslu2 running unslung. I’m listening to it right now, even as I write this. 🙂