I installed standard Debian 8.2 (jessie) / architecture i386 / kernel 3.16.0-4-686-pae on PC Engines APU.1D4
The system is configured as a dual band accesspoint equipped with Mikrotik R11e-2HPnD and R11e-5HnD.
I had to drill the case cover with 2 extra holes (opposite to the existing ones) to mount the 2 excess antennae.
Works like a charm even with the standard power supply (24W) delivered with the APU bundle.
UPDATE as of 2018_12_30:
I now even can provide an image for this thread