Here's my take on things regarding Firmware for Mini-X U9-H:
* The latest stable version is FW008. Based on my own experiences and posts on this forum this version still contains lots of bugs, even for functionality that should be very basic for a Media Player. Sound problems, power on issues, media stops playing by itself for no reason etc.
* Despite the serious bugs, FW008 has been announced as the last Android Marshmallow release (6.x).
* Mini-X has released a Beta version of Android Nougat (7.x). Based on feedback from users, it's in a really bad state. Lots of bugs. Looks more like an attempt to put a Nougat check box in comparison sheets than a serious attempt to bring out usable firmware.
* The Mini-X U9-H Nougat FW is 3 months old. No date communicated for if/when there ever will be a stable version.
* Android is now at version Pie (9.x). So Mini-X is effectively 3 Android generations behind with a stable version.
Conclusion: No stable FW exists. No stable FW on the horizon.