So the only way iv'e figured out how to find the ".mainactivity" is to run a logcat on a rooted device. But from what I'm seeing so far all the emulators that currently work with hyperspin have those arguments here in the forums or on that link you posted. The only emulators i cant get working right now are the new mupen64 alpha, and the garage games emulators. I got the launch arguments from a logcat, but for mupen it still returns emulator not found, and for mastergear (a garage game emulator) it finds the emulator and loads it, but does not load the game and leaves you at a black screen.
edit:
If anyone is curious the argument for the mupen alpha is
but it doesnt work for me