I have digitized all my music a long time ago and played through a SONOS-system. This has limited me to resample all files to max 48k/16bit because that’s the highest resolution on that gear. For CD:s which is 44.1/16bit that’s no problem, but for all my old vinyl’s as I have digitized at 48k/24bit and all new High-res stuff you can buy, that’s a limitation.
So when I came across Volumio and the Raspberry Pi, I couldn’t stay away from building a suitable housing for them. I had also an audio-switch that was put in there as well. It detects the signal from the Sonos to automatically start my amplifier and equalizer. I had a 19" cabinet laying unused that had the same with and depth as my amp and EQ.
So here we go!
First the block-diagram with a draft design. In the top left are the audio-in from Sonos. When the audio-detect circuit senses audio from Sonos, it activate´s a power relay on the mains that feeds the amp, equalizer and a 5V supply. Normally the relay-contacts put the audio out to the amp. The 5V is used to glow some LED:s. When the relay’s are activated with a switch in the front, the audio from the Pi is switched to the amp and the 5V to supply the Pi. The 5V is filtered before it feeds the Pi.
Second the completed cabinet. In the front-left there is a USB via an extension cord from the Pi. To the right there are the switches. One for starting the Pi and one for Audio detect. It can be set as (1) always on, (A) auto or (0) always off. The LED:s indicates the source. The left (blue) is Pi-audio and the right (white) is Sonos-audio.
Here is a inside view with everything wired up. As you can see, the Pi is running under test, it’s a model B with Hifi-Berry attached. Both the audio-detection and the audio-relays are built on Vero-board. Doesn’t look so nice, but no one can see that in the bookshelf 
The connections at the back is from the left to right:
ETHERNET to Pi, Control to power-relay, 12V-DC, 5V-DC, RCA-in from Sonos, RCA-out to amp.
The only design-flaw is that I have to unscrew the front-panel if I need to change the SD-card.
