Ok. Tested in BP with 100 Saw Waves (50 normal, 50 phase inverted), all I hear is the vorbis artifacts -> sample accurate playback works. Until it does not. 
Sometime a SAW wave comes through. Do you want the project do try on your end? It’s extreme but I thought breaking the system is a good way to test the system. 
A problem I still see is that for every of my called “WAV PLAYER” instances in a soundCue there is a Sound Source -> voice, so I ended up with 100 voices.
Could there be a way to do certain sound operations BEFORE the sound becomes a voice? This would make composite sound that are made up from many, many layers work better, because a certain audio amount can be mixed & built before any DSP/spatialization happens.
Thank you!