Just got my AMP+ today.
The pre-configured image does work.
I run jessie kernel Linux raspberrypi 4.1.17-v7+ and i run a lot of additional stuff on there, not wanting to set that up all over again on a clean image.
Followed all steps in the 3.x.x guide, AMP+ is identified as card 0:0, mplayer does play everything seems to be ok, except there's no sound output.
Volume output is 100% in alsamixer.