I had some trouble myself getting sounds in, so I wanted to share how I got through it.

Audio File Types
It seems that Effekseer only accepts PCM  .wav files at certain rates. I found success converting my audio files at
https://online-audio-converter.com/ (Any converter should work though) 
and rendering it as a .wav under 44.1Khz (44100Hz) :
 
[Caution] My effekseer crashed attempting  higher  quality than this, so  save your work before  experimenting with audio.

Sound OverLooping
If you have multiple spawns of an animation, it will play a sound for each spawn.
To play a sound only once regardless of other nodes and spawnrates:
[1] Create a New Node 
[2] hide the graphic portion of the node. 

(option 1) in the [Render] tab, change the Node Type from "Sprite" to "None"

(option 2) In the 'Scale' tab, reduce the scale to hide the default white-box of this new node. 

[3] Attach the sound to this new node.

I think that instead of reducing the 'Scale', it's probably more efficient to, in the Render (not Basic Render, shown as an orange cube, but Render, shown by a white cube) tab, you change the node type from the default Sprite, to None!

Good call joeseph, will edit original post!