I've spent 2 days unsuccessfully trying to install the software from the download linked from this page: Cirrus Logic Audio Card for Raspberry Pi A plus and B plus (cirrus_audio.zip 2.1GB) but now I've found a download on another page: https://www.element14.com/community/community/raspberry-pi/raspberry-pi-accessories/cirrus_logic_audio_card (cirrus_logic_audio_card_all_pi_versions.zip 1.7GB). I'm wondering if I'd be better using that. At the moment, after successfully burning the img file to a micro sd card (formatted correctly) two red lights come on as soon as I power my Pi and there's no indication the software is being accessed.
Unfortunately some of the "official" software is quite dated and not updated. So see Driver fixes and updates to kernel 3.18.16 and 4.0.5 . This person graciously updates and compiles new versions to keep up with bugs and changes. Good luck and have fun.