Wow this is a super impressive project. I was originally expecting a device built around a Raspberry Pi, but this is a completely custom designed linux board!
I don't understand why they didn't just use a pi; it would have been cheaper and easier. It already has ethernet and analog audio out.
I'd love to have time to work on something similar. My targets would be different audio-quality wise, but it's a very nice project. Kudos to its maker.