Inserting Audio only
This has been supported since very early on and is in use by some very high profile, audio-centric shows to add final audio to final picture on the day of delivery without a re-export. Audio insert only from a WAV source is described in the 1.8x quickstart on the bottom of p8 and there is a quick-and-dirty video showing WAV audio insert setup here: https://www.dropbox.com/s/orgeqkfg5d4tk4u/WAV_insert_how_to.mov.mp4?dl=0
In a nutshell, you cannot open a WAV file in the player window. You need to use the audio routing UI which is where you select the source for each channel to be inserted.