Thank you for linking this, it's probably the most functional thing I've used for doing this out of all my attempts. After testing this out, I've gotten it to partially work.
Working with the default male avatar rig, I made a test animation:
But in my viewer, it plays out like this instead:
I thought that I might've been using the wrong orientation with the avatar, so I tried rotating it and making a new, simpler animation:
But that just led to Firestorm being unable to even load the animation:
Not quite sure what I'm doing wrong here, although I do know that my Maya settings are set to use Y-Up by default.