Current Amlogic builds have limited support for DVB devices compared to Generic/RPi builds due to the ancient 3.10/3.14 kernels in use and we are still experimenting with media_build support. We figured out how to backport and build it, but this then breaks other drivers (e.g. IR things) we consider to be more fundamental and important. If you find something that works, great, but if not an RPi3 as the headend device is a good compromise.
NB: Things will improve for 64-bit devices once we move up to a current kernel as we'll be able to use media_build without hacking, but that's months away and 32-bit hardware will remain on the older kernels (noticing one of your boxes is S805).