I'm happy with my MINI MX-G but I have to use two LE version on two SD card (one for view pictures and one for watch movies) because the S905 has not enough power to render 4k GUI.
I hoped the S912 will solve this problem but without you and your LE version the S912 is just another cheap chinese junk.
The S912 is basically a rip off in my mind. The only reason box makers are putting it in their boxes is to make a buck off people who don't read the specs. There is no real advantage over the S905X for watching videos or viewing pictures, yet it costs much more because of the increased core count and "gaming" GPU.. Bottom line is if you want a premium TV box you are better off spending your money on a well-supported S905 box like the Wetek Hub rather than a generic S912 box. The problem you are facing is more likely related to software limitation/bugs than hardware. The hardware of the S905 is capable of 4k.
Another factor is that all of this development is tied to what is going on with the Wetek boxes and the Odroid. Neither of those players are jumping at the S912 (because it is a stupid chip to put in a TV box) so there is no development happening whatsoever for that chip and I wouldn't expect any in the future. If Odroid or Wetek build anything with the S912 I will be very surprised.