My CD-collection is digitised on a hard disk and I have built a music-player around Raspberry Pi B+ hardware and Volumio-software (https://volumio.org/). RaspPi was connected to my Cambridge Audio DacMagic Plus DAC with USB-audio connection. Now I updated Volumio from 1.4 to version 1.5 and upgraded the RasbPi with HifiBerry Digi+ expansion board. This board adds SPDIF and optical TOSLINK connections to RasbPi. I have had this HifiBerry expansion for some time but it didn't work with Volumio 1.4/RasbPi B+ combination (at least not as plug-and-play). With Volumio 1.5 this combination works flawlessly. In Volumio's System-settings I choose I2S DAC as Hifiberry Digi. After this Playback-settings shows that Audio Output is changed to sndrpihifiberry. Hifiberry's TOSLINK is connected to Cambridge Audio DAC so the audio-stream is now fully digital from RasbPi to external DAC. Quality difference is not huge but I can hear how the stereo-field is now bigger and deeper than before with the USB-connection.
I needed also a new bigger case for RasbPi where the HifiBerry-expansion
fits nicely. This case is a simple laser-cut case that consists of 6
plastic pieces that are clicked together.