Please note that running
as described in https://www.hifiberry.com/docs/archive/hifiberry-software-configuration/ should be
sudo rpi-update FIRMWARE_VERSION
where FIRMWARE_VERSION is the GitHub commit hash belonging to the specific version of the operating system installed. This can be found at https://github.com/Hexxeh/rpi-firmware/commits/master and should match kernel version, or additional commits without bumping to a new kernel version.
Omitting this version number will install the latest version of the firmware which can also be a testing version and can result that the system is not working anymore, at least regarding the audio part.
See also https://downloads.raspberrypi.org/raspbian/release_notes.txt for firmware versions and https://github.com/Hexxeh/rpi-update for more on rpi-update.