I have the AMP2 and my pi working currently, but am having an issue with volume. If I play music, then pause it for 10 or 15 seconds, then play it again, it plays at maximum volume.
I am using bluetooth from my phone to play the music, set up with https://github.com/BaReinhard/Super-Simple-Raspberry-Pi-Audio-Receiver-Install , as this is the only way I've found to actually get audio to play back through the pi via bluetooth. In the setup I used option 2, DAC Standard/Pro, as the documentation says to treat the AMP2 as a DAC+.
On the pi, the volume icon does not work, it says "No volume control on this device" when clicked. I can adjust the volume using sudo amixer set Master X%, but again if I pause the music long enough then start playing again it comes through at full volume. This also ignores the volume setting on the phone.