I thought I'd share details of my HiFiBerry installation.
I paired up a HiFiBerry with an RPI B+, and installed the latest Volumio image on the RPI. This was a build as a present for my girlfriend, so I spent some time looking for the right case, before I decided on the Q6 Mini-Itx case.
The case is quite nice looking, of good construction in black anodised aluminium and comes with a power supply, start button and various other bits and pieces. It comes without a back panel, since you're supposed to buy that separately (depending what board you want to put in there).
I also bought a WD Elements 1Tb USB3 portable hard drive, a D-Link powered 4-port hub, an Edimax N150 Nano wireless USB adapter and a sheet of black anodised aluminium from eBay!
I also bought an ATX Raspi board from Low Power labs to handle the on/off switch on the case.
I started by removing all the internals of the Q6 case, leaving only the power switch at the front (along with its connectors) and de-soldered the power connections from the socket in the case. I then cut the anodised aluminium sheet down to size and cutting holes for two RCA audio out connectors and a slot for the wireless USB adapter. I glued this into the back of the case. I made a couple of RCA flyleads and soldered them to the tags on the RCA connectors on the back of the case.
I then cut the end off the external power supplies that came with the case and the USB hub and fixed the case's power plug onto the usb hub's power supply, so I could plug it neatly into the case. I then soldered the trailing lead and plug from the USB hub onto the terminals on the case's socket, earthing it on a convenient case screw hole left when I removed the VESA gubbins from inside the case!
I cut some expanded foam packing material down to size and glued it into the case as a base for mounting the components. I installed everything into the case, with the incoming power plugged into the USB hub. I then used a USB-to-micro-usb lead to connect the hub to the ATX raspi board to power it (one of the reasons I selected this hub is that it supplies power across all the ports!). I connected the external hard drive to another port on the hub, then the hub to the RPI using a type-b to usb type A lead. I also made a short usb-plug-to-socket cable and glued it into the back plate, so the wireless adapter could just be plugged straight into the back of the case from the outside. I plugged the RCA flyleads into the HiFiBerry, obviously!
The ATX Raspi is designed to control the flow of power to the RPI, so I soldered the (supplied) USB socket to the Raspi, and used this with a usb-to-micro-usb lead to connect to the RPI. I snipped off the "HDD Led" connector on the case and connected the "Power Switch" and "Power LED" connectors to the Raspi.
Finally, I soldered a couple of two-pin headers to both the ATX Raspi and the HifiBerry's pass-through GPIO header socket, connecting GPIO 7 and 8 to the two control pins on the Raspi.
And voila! A compact, good-looking wireless audio streamer, with a single, neat external power supply. The case switch starts up the device (it takes a little while to boot Volumio, but when it's ready it makes quite a nice little startup sound through the hifi!). When you want to switch it off, hold down the power button for 4 seconds. The blue led starts to pulsate as the RPI shuts down, gets faster as it approaches shutdown, then goes out. This has the nice side benefit of safely unmounting your SD card and avoiding a corrupted image.
I paired up the device with a Cambridge Audio Topaz AM1 amp, Wharfedale Diamond 9 speakers and - because my girlfriend loves vinyl - a Sony PSLX300 turntable.
All in all, a pretty sophisticated setup at a decent price.
Here are some pictures of the device (I know there is a lot of cabling in there - if I'd had shorter cables, I'd have used them!):
Hopefully all this is of use to anyone else planning to do this kind of thing. Ask me if you have any questions.