i just got a Hi-FiBerry Amp+ and its working fine apart from the equaliser has absolutely no effect on the sound. I put some of them on 100 and some on 0 and it makes absolutely no difference.
I'm running on the following:
Raspberry Pi 3
Raspbian GNU/Linux 8 (jessie) Linux 4.4.50-v7+ #970
**** List of PLAYBACK Hardware Devices ****
card 0: sndrpihifiberry [snd_rpi_hifiberry_amp], device 0: HifiBerry AMP HiFi tas5713-hifi-0 
Subdevice #0: subdevice #0
Thanks in advance