Brief update, which has less to do with amlogic boards, but with hyperion: I've bought a Rasp Pi 3 B+ (the new 1.4GHz model) and, as expected, Hyperion is working flawslessly (with framegrabber of course).
Can it read HEVC? yes, very well now (tried movies with and over 12Mb/s, all OK)
Can it handle 4K? no, of course (but hyperion has problems with 4K anyway)
So, if you are still struggling with hyperion and dont care about 4K, this could be a cheap solution