I've finally gotten this (com_mvas_stbemu_pro-10071232.apk) configured on my Amazon FireTV. I like to support developers, so it's the paid version. I downloaded the apk using "Raccoon" (Google it)
I don't know if these settings will work for anyone else, but here are my configuration steps that worked:
1) Uninstalled the previous version then open the newly-installed app,
2) Hit the menu button on the AFTV remote and selected "Settings"
3) Went to "Profiles" and filled the following fields:
a) Changed Profile name to whatever I wanted
b) Entered MAC address from my Donation
c) Entered 13-character Serial number with one capital letter
d) Used a Minix A2 USB Mouse/Keyboard/Remote to scroll down to "Device" (A regular mouse or keyboard might work -- no clue...)
e) Entered the 64-character SHA256 alphanumeric "Device ID" that I calculated using "Serial-MAC_Address-Donation#" (FTR, this is the same calculated Device ID I use in KODI.)
f) Clicked "Send Device ID"
4) Backed out to the main menu where it asks for the username and password
5) Hit the menu button on the AFTV remote again and this time selected "Keyboard" (This makes the Amazon keyboard pop up)
6) Quickly entered the Donation # and hit "Submit" then down-direction to "Password" and quickly entered Donation# again
7) Down-direction on AFTV remote to "OK" and the progress bar started making progress
8) Backed out to AFTV Settings and "Force Quit" STB Emulator Pro
9) Pulled power cord from AFTV then rebooted.
PROFIT!!!
Currently, I'm using IJK Player but I've noticed a weird thing on either non-external player: The only way I can get to a full-screen picture is once I have a channel playing, I need to hit "Enter" then right-direction and left -direction back to the channel, then hit "Enter" again. From then on, the full-screen toggles correctly when the "Enter" button is pressed.
If someone has a trick for quickly getting into full-screen mode, I sure would appreciate the info share.